^ hmm., it is a simple thing. there should be no need of a plugin!
All you have to do is get the "MySubscriptions" plugin like i have, set it up and the subscriptions
Then go to your Forums Root and make a copy of any php file, open it up.. delete all the content in it then put this code in there:
<?php
header( 'Location: http://pulsiveforums.net/misc.php?action=payments' ) ;
?>
Now save it, and rename the file "Upgrade.php"