Module development and code questions

Exists a function to get node info (object) passing the nid to a parameter?

Exist a function to check if module is installed?

Is there any module that processes a RTF format into a PDF format?

Is there any module that processes a RTF format into a PDF format?

I'm working on a module to implement a d20 character sheet and I'd like to pretty up the input form. For some reason, I can't seem to figure out how to apply a theme to the form. The base name of my module is "characters." Here's what I think is the relevant code

<?php
function characters_form(&$node) {

... // snip

// str
$form['attributes']['STR']['permstr'] = array(
'#type' => 'textfield',
//'#title' => t('STR'),
'#required' => TRUE,
'#default_value' => $node->str,
'#size' => 3
);
$form['attributes']['STR']['tempstr'] = array(
'#type' => 'textfield',
//'#title' => t('Temp STR'),
'#required' => FALSE,
'#default_value' => $node->tempstr,
'#size' => 3
);

// dex
$form['attributes']['DEX']['permdex'] = array(
'#type' => 'textfield',
//'#title' => t('DEX'),
'#required' => TRUE,
'#default_value' => $node->dex,
'#size' => 3
);
$form['attributes']['DEX']['tempdex'] = array(
'#type' => 'textfield',
//'#title' => t('Temp DEX'),
'#required' => FALSE,
'#default_value' => $node->tempdex,
'#size' => 3
);

// con
$form['attributes']['CON']['permcon'] = array(
'#type' => 'textfield',
//'#title' => t('CON'),
'#required' => TRUE,

I am working on a module that will allow multiple users to have superuser access (uid 1 access).

Eventually, this code will be moved to a module, but for now I am modifying the core to make sure my code is right. PLEASE DO NOT POST HERE TELLING ME THAT CORE HACKING IS A BAD IDEA... I know that... this is temporary.

I added a few lines to user_access() which is in modules/user/user.module. The SQL query there will return a single column and single row with the value "superuser" if the user id in question has been assigned the role "superuser." If not, the SQL query should return an empty set. After adding this code in, I am getting a ton of errors that all say: user warning: Query was empty query: [snip/]. Can anyone tell me how to avoid this error?

function user_access($string, $account = NULL) {
global $user;
static $perm = array();

if (is_null($account)) {
$account = $user;
}

// User #1 has all privileges:
if ($account->uid == 1) {
return TRUE;
}

/********** START MY CODE **********/
// Users with role 'superuser' have all privileges
$is_superuser_query = "SELECT DISTINCT(sr.name) FROM {users_roles} ur, {shared_role} sr WHERE ur.uid=$account->uid and ur.rid = sr.rid and sr.name = 'superuser';";
$is_superuser = db_query($check_if_superuser_query);
if ($is_superuser) {
return TRUE;
}