Quick question on customizing this script..

<?php

/**
* A simple visitor tracking script for use on multiple sites (a network).
*
* Copyright 2004 Peter Cowburn <peter@cowburn.info>
*
* Examples:
*      http://logohq.net/misc/code/php_counter/
*      http://logohq.net/misc/code/php_counter/?site=mysite
*      http://logohq.net/misc/code/php_counter/?site=other
*
* Any additions/modifications/distribution of this material is
* allowed without contacting the original author or crediting of the
* original author.
*/

/**
* A simple error handling function
*
* @param     string            $str     Message to be displayed.
* @param     string/integer    $line    (Optional) Line number of error.
* @return    void                       Prints error message and halts all processing.
*/
function mysql_die($str, $line=null) {
  $friendly = 'An error has occured and all page processing has been halted.';
  if ($line !== null) {
    $str = 'Line ' . $line . ': ' . $str;
  }
  $msg = sprintf('<p>%s</p><code>%s</code>', $friendly, $str);
  die ($msg);
}

// holder for mysql preferences
// *** CHANGE THESE! ***
$mysql = array (
  'host'  => 'mysql.mynetwork.com', // or, localhost?..
  'user'  => 'username',
  'pass'  => 'password',
  'db'    => 'dbCounter',
  'table' => 'tCount'
);

// holder for our visitor's data
$data = array (
  'ip'   => $HTTP_SERVER_VARS['REMOTE_ADDR'],
);


// Information for "default" hits
$default_site = array (
  'key'  => 'yaxay',
  'name' => 'yaXay.com'
);

// Allowing other sites in on the act (via query string)
// Follows pattern:
//   mysql_store_name => html_display_name
$sites = array (
  'mysite'  => 'www.MySite.com',
  'other'   => 'www.MyOtherSite.com'
);

if (($_GET['site'] == '') || (array_key_exists($_GET['site'], $sites) === false)) {
  $site_key  = $default_site['key'];
  $site_name = $default_site['name'];
} else {
  $site_key  = preg_replace('#[^a-zA-Z0-9_]+#', '', $_GET['site']);
  $site_name = $sites[$site_key];
}

// holder for general preferences
$prefs = array (
  // how long do we recognise a "visitor" for? (minutes)
  'timeout'      => 15,
  // site name in the DB
  'tSite'        => $site_key,
  // Friendly site name
  'fSite'        => $site_name,
  // Friendly network name
  'fNet'         => 'MyNetwork',
  // Friendly message
  'fMess'        => '<p>Visitor count for %s: %d</p>',
  // Show friendly messages? (true/false)
  'showMessages' => true
);

// Holder for our visitor counts
$count = array (
  'site' => 0,
  'net'  => 0
);

// Connect to host and DB
$conn =  mysql_connect($mysql['host'], $mysql['user'], $mysql['pass'])
  or mysql_die('Cannot connect to database host.', __LINE__);

$db = mysql_select_db($mysql['db'], $conn)
  or mysql_die('Could not select database to retrieve data.', __LINE__);

// Check if the user has already been logged and is still "active"
$sql = sprintf("SELECT * FROM %s WHERE ip='%s' AND site='%s' AND DATE_SUB(NOW(),INTERVAL %s MINUTE)<=stamp;", $mysql['table'], $data['ip'], $prefs['tSite'], $prefs['timeout']);
$result = mysql_query($sql, $conn) or mysql_die('Could not check visitor table.', __LINE__);

if (mysql_num_rows($result) > 0) {
  $record = mysql_fetch_object($result);
  // Visitor already here... so update to current time
  $sql = sprintf("UPDATE %s SET stamp=NOW() WHERE site='%s' AND ip='%s' AND stamp='%s';", $mysql['table'], $prefs['tSite'], $data['ip'], $record->stamp);
  mysql_query($sql, $conn) or mysql_die('Could not update timestamp.', __LINE__);
} else {
  // A new visitor, so lets add them
  $sql = sprintf("INSERT INTO %s SET ip='%s', site='%s';", $mysql['table'], $data['ip'], $prefs['tSite']);
  mysql_query($sql, $conn) or mysql_die('Could not log visitor.', __LINE__);
}


// Now lets count our active users on the site...
$sql = sprintf("SELECT COUNT(ip) as total FROM %s WHERE site='%s' AND DATE_SUB(NOW(),INTERVAL %s MINUTE)<=stamp;", $mysql['table'], $prefs['tSite'], $prefs['timeout']);
$result = mysql_query($sql, $conn) or mysql_die('Error gathering local stats.', __LINE__);
$count['site'] = mysql_result($result, 0);

// ... and on the entire network!
$sql = sprintf("SELECT COUNT(ip) as total FROM %s WHERE DATE_SUB(NOW(),INTERVAL %s MINUTE)<=stamp;", $mysql['table'], $prefs['timeout']);
$result = mysql_query($sql, $conn) or mysql_die('Error gathering network stats.', __LINE__);
$count['network'] = mysql_result($result, 0);

// If we chose to show the counts
if ($prefs['showMessages'] == true) {
  // Tell the world what we have found out!
  printf($prefs['fMess'], $prefs['fSite'], $count['site']);
  printf($prefs['fMess'], $prefs['fNet'], $count['network']);
}

// Don't forget to close the DB connection
@mysql_close($conn);

// And finish.
exit;

?>