Registering Variables Help

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Hey all i have a php script for random ads

PHP Code:

<?php 
$fcontents = join ("", file ("http://www.myanimeisland.com/banner_ads.txt")); 
$s_con = split("~",$fcontents); 
$banner_no = rand(0,(count($s_con)-1)); 
echo $s_con[$banner_no]; 
?>

I uploaded with the Txt file checked the URL and it works great

i than added a plugin in vbulletin

PHP Code:

ob_start();
  include('/home/**********/public_html/banner.php');
  $bannerphp = ob_get_contents();
  ob_end_clean(); 


Run of the Hook Global_start

i than added

{vb:raw bannerphp}

in my template and it didnt show
i read the vb manual some more and found that in vb 4 you need to Registering Variables

PHP Code:

vB_Template::preRegister('FORUMHOME',array('includedphp ' => $includedphp)); 


Where would i but this ? ive tryed everywhere and it will not show my banners

Thanks alot