[aeturner89]

Easily.

Make one forum and give the payments usergroup access only to it and for every other usergroup you don't want access to, disallow them from viewing the forum with forum permissions.

Then make another forum with the same name with regular permissions. Place it under the first and disallow the payments usergroup of seeing it.

When you add the form where it says

Forum Link (Entering a URL here will cause anyone clicking the first forum but the second forum which has the link to be redirected to that URL)

put http://www.yoursite.com/forums/payments.php

Then anybody who's not on the paid usergroup won't see that forum but everyone else will see the redirect.