Confused about Pro-Sites and Marketpress compatibility

Hey there!

I'm just a little confused as to what I'm supposed to do to get both pro sites and marketpress working in tandem. I'm running a multisite marketpress on the paypal express global cart. I'm trying to allow upgraded memberships via pro sites (extra upload space, membership fees). Is there a need use this IPN forwarding script ive read about?
i did have supporter before although i never set it up entirely. I believe i deleted all of the files.

Any information helps!

Thanks guys