Want to offer free membership, but not thru Prosites

I currently have Prosites configured as "pay to blog." In other words, I don't want to offer any free site, but I would like to simultaneously offer a free membership for people to participate in the Buddy Press community and have access to special protected pages of content.

I previously tried to configure the Membership plugin and Prosites and they did not work well together, especially the registration part.

I don't understand Buddy Press yet, but I do have it installed, but not functioning.

What would you suggest for what I want to accomplish: Prosites active for site creation, and something else for free memberships?

Thanks, Joe.