getting rid of username display and replacing it with a custom profile field in blog module

The blog module does not use theme('username',$user) where it should. I replaced all $user->name with check_plain(theme('username',$user)) or $node->name with check_plain(theme('username',$node)), where username is ment.

Also did it with $account->name in blog.pages.inc.

This is for Drupal 6.x. In Drupal 5.x it might be theme_username($user).

FIXING ONE PROBLEM WITH THIS... HOLD UP!

So in the best possible Drupal world we abstract the username. I choose to control this in the template file. This is where the node_profile module does it along with usernode. There you can set it to: the title of the usernode, the concatenation of two profile fields, a cck usernode fullname field, or anything you want. Then call the theme('username',$user) function anytime you need it. To do this (especially from the blog module) you'll need to add another little feature to the template file defining the theme function to return a display name THAT'S NOT A LINK. That theme function call will look this like this: theme('username',$user,false).

Add this line to your username function...
function phptemplate_username($object, $link=true) {

Then this one...

// There are several options to use as user's display name
// $userNode->title OR $object->name OR $user->profile_fullname
// There are of course various ways to set up user profiles. I use usernode...
// 'node/'. $userNode->nid
if($link) $output = l(NAME HERE, PROFILE URL HERE, array('title' => t('View user details.')));
else $output = $userNode->title;

Now that template is allowing you to get a user's display name via a theme function, you can pull that into your blog module.
Here is the blog.module file all updated for you.

<?php
// $Id: blog.module,v 1.271.2.2 2007/04/23 17:05:11 dries Exp $

/**
 * @file
 * Enables keeping an easily and regularly updated web page or a blog.
 */

/**
 * Implementation of hook_node_info().
 */
function blog_node_info() {
  return array(
    'blog' => array(
      'name' => t('Blog entry'),
      'module' => 'blog',
      'description' => t('A blog is a regularly updated journal or diary made up of individual posts shown in reversed chronological order. Each member of the site may create and maintain a blog.'),
    )
  );
}

/**
 * Implementation of hook_perm().
 */
function blog_perm() {
  return array('edit own blog');
}

/**
 * Implementation of hook_access().
 */
function blog_access($op, $node) {
  global $user;

  if ($op == 'create') {
    return user_access('edit own blog') && $user->uid;
  }

  if ($op == 'update' || $op == 'delete') {
    if (user_access('edit own blog') && ($user->uid == $node->uid)) {
      return TRUE;
    }
  }
}

/**
 * Implementation of hook_user().
 */
function blog_user($type, &$edit, &$user) {
  if ($type == 'view' && user_access('edit own blog', $user)) {
    $items['blog'] = array('title' => t('Blog'),
      'value' => l(t('View recent blog entries'), "blog/$user->uid", array('title' => t("Read ".check_plain(theme('username',$user,false))."'s latest blog entries.", array('@username' => check_plain(theme('username',$user,false)))))),
      'class' => 'blog',
    );
    return array(t('History') => $items);
  }
}

/**
 * Implementation of hook_help().
 */
function blog_help($section) {
  switch ($section) {
    case 'admin/help#blog':
      $output = '<p>'. t('The blog module allows registered users to maintain an online weblog (commonly known as a blog), often referred to as an online journal or diary. Blogs are made up of individual posts that are time stamped and are typically viewed by date as you would a diary. Blogs often contain links to web pages users have read and/or agree/disagree with.') .'</p>';
      $output .= '<p>'. t('The blog module adds a <em>user blogs</em> navigation link to the site, which takes any visitor to a page that displays the most recent blog entries from all the users on the site. The navigation menu has a <em>create a blog entry</em> link (which takes you to a submission form) and a <em>view personal blog</em> link (which displays your blog entries as other people will see them). The blog module also creates a <em>recent blog posts</em> block that can be enabled.') .'</p>';
      $output .= '<p>'. t('If a user has the ability to post blogs, then the import module (news aggregator) will display a blog-it link next to each news item in its lists. Clicking on this takes the user to the blog submission form, with the title, a link to the item, and a link to the source into the body text already in the text box, ready for the user to add a comment or explanation. This actively encourages people to add blog entries about things they see and hear elsewhere in the website and from your syndicated partner sites.') .'</p>';
      $output .= '<p>'. t('For more information please read the configuration and customization handbook <a href="@blog">Blog page</a>.', array('@blog' => 'http://drupal.org/handbook/modules/blog/')) .'</p>';
      return $output;
  }
}

/**
 * Displays an RSS feed containing recent blog entries of a given user.
 */
function blog_feed_user($uid = 0) {
  global $user;

  if ($uid) {
    $account = user_load(array('uid' => $uid, 'status' => 1));
  }
  else {
    $account = $user;
  }

  $result = db_query_range(db_rewrite_sql("SELECT n.nid, n.created FROM {node} n  WHERE n.type = 'blog' AND n.uid = %d AND n.status = 1 ORDER BY n.created DESC"), $uid, 0, variable_get('feed_default_items', 10));
  $channel['title'] = check_plain(theme('username',$user,false)) ."'s blog";
  $channel['link'] = url("blog/$uid", NULL, NULL, TRUE);
  $channel['description'] = $term->description;
  node_feed($result, $channel);
}

/**
 * Displays an RSS feed containing recent blog entries of all users.
 */
function blog_feed_last() {
  $result = db_query_range(db_rewrite_sql("SELECT n.nid, n.created FROM {node} n WHERE n.type = 'blog' AND n.status = 1 ORDER BY n.created DESC"), 0, variable_get('feed_default_items', 10));
  $channel['title'] = variable_get('site_name', 'Drupal') .' blogs';
  $channel['link'] = url('blog', NULL, NULL, TRUE);
  $channel['description'] = $term->description;
  node_feed($result, $channel);
}

/**
 * Menu callback; displays a Drupal page containing recent blog entries.
 */
function blog_page($a = NULL, $b = NULL) {

  if (is_numeric($a)) { // $a is a user ID
    if ($b == 'feed') {
      return blog_feed_user($a);
    }
    else {
      return blog_page_user($a);
    }
  }
  else if ($a == 'feed') {
    return blog_feed_last();
  }
  else {
    return blog_page_last();
  }
}

/**
 * Displays a Drupal page containing recent blog entries of a given user.
 */
function blog_page_user($uid) {
  global $user;

  $account = user_load(array((is_numeric($uid) ? 'uid' : 'name') => $uid, 'status' => 1));

  if ($account->uid) {
    drupal_set_title($title = t(check_plain(theme('username',$user,false))."'s blog", array('@name' => check_plain(theme('username',$user,false)))));

    if (($account->uid == $user->uid) && user_access('edit own blog')) {
      $output = '<li>'. l(t('Post new blog entry.'), "node/add/blog") .'</li>';
    }
    else if ($account->uid == $user->uid) {
      $output = '<li>'. t('You are not allowed to post a new blog entry.') .'</li>';
    }

    if ($output) {
      $output = '<ul>'. $output .'</ul>';
    }
    else {
      $output = '';
    }

    $result = pager_query(db_rewrite_sql("SELECT n.nid, n.sticky, n.created FROM {node} n WHERE n.type = 'blog' AND n.uid = %d AND n.status = 1 ORDER BY n.sticky DESC, n.created DESC"), variable_get('default_nodes_main', 10), 0, NULL, $account->uid);
    while ($node = db_fetch_object($result)) {
      $output .= node_view(node_load($node->nid), 1);
    }
    $output .= theme('pager', NULL, variable_get('default_nodes_main', 10));
    drupal_add_feed(url('blog/'. $account->uid .'/feed'), t('RSS - !title', array('!title' => $title)));

    return $output;
  }
  else {
    drupal_not_found();
  }
}

/**
 * Displays a Drupal page containing recent blog entries of all users.
 */
function blog_page_last() {
  global $user;

  $output = '';

  $result = pager_query(db_rewrite_sql("SELECT n.nid, n.created FROM {node} n WHERE n.type = 'blog' AND n.status = 1 ORDER BY n.sticky DESC, n.created DESC"), variable_get('default_nodes_main', 10));

  while ($node = db_fetch_object($result)) {
    $output .= node_view(node_load($node->nid), 1);
  }
  $output .= theme('pager', NULL, variable_get('default_nodes_main', 10));
  drupal_add_feed(url('blog/feed'), t('RSS - blogs'));

  return $output;
}

/**
 * Implementation of hook_form().
 */
function blog_form(&$node) {
  global $nid;
  $iid = $_GET['iid'];
  $type = node_get_types('type', $node);


  if (empty($node->body)) {
    /*
    ** If the user clicked a "blog it" link, we load the data from the
    ** database and quote it in the blog:
    */

    if ($nid && $blog = node_load($nid)) {
      $node->body = '<em>'. $blog->body .'</em> ['. l($blog->name, "node/$nid") .']';
    }

    if ($iid && $item = db_fetch_object(db_query('SELECT i.*, f.title as ftitle, f.link as flink FROM {aggregator_item} i, {aggregator_feed} f WHERE i.iid = %d AND i.fid = f.fid', $iid))) {
      $node->title = $item->title;
      // Note: $item->description has been validated on aggregation.
      $node->body = '<a href="'. check_url($item->link) .'">'. check_plain($item->title) .'</a> - <em>'. $item->description .'</em> [<a href="'. check_url($item->flink) .'">'. check_plain($item->ftitle) ."</a>]\n";
    }

  }

  $form['title'] = array('#type' => 'textfield', '#title' => check_plain($type->title_label), '#required' => TRUE, '#default_value' => $node->title, '#weight' => -5);
  $form['body_filter']['body'] = array('#type' => 'textarea', '#title' => check_plain($type->body_label), '#default_value' => $node->body, '#rows' => 20, '#required' => TRUE);
  $form['body_filter']['filter'] = filter_form($node->format);
  return $form;
}

/**
 * Implementation of hook_view().
 */
function blog_view($node, $teaser = FALSE, $page = FALSE) {
  if ($page) {
    // Breadcrumb navigation
    $breadcrumb[] = array('path' => 'blog', 'title' => t('Blogs'));
    $breadcrumb[] = array('path' => 'blog/'. $node->uid, 'title' => t(check_plain(theme('username',$user,false))."'s blog", array('@name' => check_plain(theme('username',$user,false)))));
    $breadcrumb[] = array('path' => 'node/'. $node->nid);
    menu_set_location($breadcrumb);
  }
  return node_prepare($node, $teaser);
}

/**
 * Implementation of hook_link().
 */
function blog_link($type, $node = NULL, $teaser = FALSE) {
  $links = array();

  if ($type == 'node' && $node->type == 'blog') {
    if (arg(0) != 'blog' || arg(1) != $node->uid) {
      $links['blog_usernames_blog'] = array(
        'title' => t(check_plain(theme('username',$user,false))."'s blog", array('@username' => check_plain(theme('username',$user,false)))),
        'href' => "blog/$node->uid",
        'attributes' => array('title' => t("Read ".check_plain(theme('username',$user,false))."'s latest blog entries.", array('@username' => check_plain(theme('username',$user,false)))))
      );
    }
  }

  return $links;
}

/**
 * Implementation of hook_menu().
 */
function blog_menu($may_cache) {
  global $user;
  $items = array();

  if ($may_cache) {
    $items[] = array('path' => 'blog', 'title' => t('Blogs'),
      'callback' => 'blog_page',
      'access' => user_access('access content'),
      'type' => MENU_SUGGESTED_ITEM);
    $items[] = array('path' => 'blog/'. $user->uid, 'title' => t('My blog'),
      'access' => user_access('edit own blog'),
      'type' => MENU_DYNAMIC_ITEM);
  }

  return $items;
}

/**
 * Implementation of hook_block().
 *
 * Displays the most recent 10 blog titles.
 */
function blog_block($op = 'list', $delta = 0) {
  global $user;
  if ($op == 'list') {
    $block[0]['info'] = t('Recent blog posts');
    return $block;
  }
  else if ($op == 'view') {
    if (user_access('access content')) {
      $result = db_query_range(db_rewrite_sql("SELECT n.nid, n.title, n.created FROM {node} n WHERE n.type = 'blog' AND n.status = 1 ORDER BY n.created DESC"), 0, 10);
      if (db_num_rows($result)) {
        $block['content'] = node_title_list($result);
        $block['content'] .= '<div class="more-link">'. l(t('more'), 'blog', array('title' => t('Read the latest blog entries.'))) .'</div>';
        $block['subject'] = t('Recent blog posts');
        return $block;
      }
    }
  }
}
?>