template.php

I'm a little confused by how to handle the customized features of authcache, and was wondering if a guru might be able to lend a hand.

I call my login and user information in template.php. Here is my code:

function theme_user_bar() {
  global $user;
  $output = '';

  if (!$user->uid) {
    $output .= drupal_get_form('user_login_block');
  }
  else {
    $output .= t('<p class="user-info">Welcome back!</p>', array('!user' => theme('username', $user)));
 
    $output .= theme('item_list', array(
      l(t('Your account'), 'user/'.$user->uid, array('title' => t('My account'))),
      l(t('Sign out'), 'logout')));
  }

  $output = '<div id="user-bar">'.$output.'</div>';

  return $output;
}

I don't understand how I can alter that for $user_link to handle the customized user content? I would really appreciate any help I could get.