Hi jwind,
You might want to consider S2 Member plugin that can restrict access to certan pages. It is straight forward to set up and there is also some integration with BBpress roles.
For each member you have to set the level of S2 membership, default S2 comes with 4 membership levels and you can assign different access levels to pages and so on.
Another feature is URI access restrictions which should be able to restrict access in the forums.
Instead of an error 404 the users are told that they have to sign in to view the protected contents.
/Lars
