Restricting access to site members only

If you have your member management system integrated with WWF so users use the same login and password for both, then it should be pretty easy to do if you take a slightly different approach.

Simply change the permissions of each forum area so that guests and the  non-members group cannot access the forum areas you want to block, instead of trying to block the whole forums.

When someone becomes a member, change the group they are in in WWF.  You could so this with a simple database update query.

Using this approach will allow you to have some forums for members only, and some not (if you wanted to).  You have more flexibility that way.  You could also show what forums are available without actually showing what's inside, which can help sales, because people get curious about what's inside the locked forums they can't see unless they are a member.