Don't know if you saw my detailed post about this integration issue on the .com forum, but the solution could lie either on the vb or the pp side. At the moment it's up to admins to figure out how to handle it. Since I have only the most very basic grasp of php, my solution for the moment (other than bringing it up to the developers on both sides, since this is a very common integration) was to create extra pages and copy the html for the subscriptions form -- in pieces -- into the various pages, then see if I can figure out how to restrict access to those pages.
Little baby steps.
Jeniffer