By the way, you should filter that id variable there and make sure that it contains only the path to files you have explicitly defined. For example:
<?php
$clean = array();
switch ($_GET['id'])
{
case 'edit_advantages/edit_advantages_quality.htm':
case 'edit_advantages/edit_advantages_warranty.htm':
case 'edit_advantages/edit_advantages_upgrade.htm':
case 'edit_advantages/edit_advantages_maintenance.htm':
case 'edit_advantages/edit_advantages_expertise.htm':
case 'edit_advantages/edit_advantages_support.htm':
$clean['id'] = $_GET['id'];
break;
}
?>
Then, in the rest of your script, use only $clean['id'] and not $GET['id'], since $GET['id'] should be considered tainted and contain possibly malicious data.
If you want more information about this, send me a PM, and I'll show you why this is important.