Segítene valaki? PHP

Adott egy regisztrációs script a gond vele a névellenőrzésben van. Akárhányszor újra beregisztrálja ugyanazt a nicket:

"<?php

include('PATHtoYOUR/chat/lib/data/users.php');

//check existing users

if ($_POST['username'])

{

//if user entered a name

}

//collect information from users.php

$user_amount = count($users);

for ($i=0; $i <=$user_amount;$i++);

{

//check usage of name

if (strtolower($_POST['username']) == strtolower($users[$i]['userName']))

$username_used = 1;

}

//make sure user chose a password

if (!$_POST['password'])

$password_error = 1;

//ensure username avalible and password chosen

if (!$username_used and !$password_error)

{

//present user id accepted message

print 'Your selection '.$_POST['username'].' was accepted... your account was created. You may now login!!!';

$next_user = $user_amount++;

$new_user_information = '

//remote created from '.$_SERVER['REMOTE_ADDR'].'

$users['.$next_user.'] = array();

$users['.$next_user.'][\'userRole\'] = AJAX_CHAT_USER;

$users['.$next_user.'][\'userName\'] = \''.$_POST['username'].'\';

$users['.$next_user.'][\'password\'] = \''.$_POST['password'].'\';

$users['.$next_user.'][\'channels\'] = array(0,1);

?>';

$file_edit = fopen('PATHtoYOUR/chat/lib/data/users.php', 'r+');

fseek($file_edit, -3,SEEK_END);

fwrite($file_edit, $new_user_information);

fclose($file_edit);

}

//end of php

?>

<table border="0" align="center">

<table border="0" align="center">

<tr>

<td>Use the form below to create a Chat user account.</td>

</tr>

<tr>

<td>

<!-- collect username and password information via form -->

<form action="" method="post">

Username:<input name="username" type="text" value="" /> 16 Character Maximum<br>

Password:<input name="password" type="text" value="" /> No requirements.<br>

<input name="submit" type="submit" value="Create" />

</form>

</td>

</tr>

</table>

</table>"