Question about calling PHP functions within a thread

[MoH672]

I want to be able to display information in a thread using PHP... I've figured out that I can't use PHP within the thread itself because it will not display, so I am using an iframe to call up the file which I am calling iframe.php.

This is the code I am currently testing:

PHP Code:

<?php
if ( $post[usergroupid] == 5 ) {
    echo "<font face='Tahoma' size='4' color='#FFFFFF'>This is a test using iframes and 
php functions.</font>";
}
else {
    echo "<font face='Tahoma' size='4' color='#FFFFFF'>You do not have permission to 
access this page.</font>";
}
?>

Now, I am a member of Usergroupid 5 however it is displaying the else statement instead of showing me the info I want. Do I need to use some PHP command that links my statements? I am sort of figuring that the PHP doesn't know what $post[usergroupid] is, but I don't know how to link it to all the other vBulletin information.

Help appreciated!