As per our chat tonight, I experimented with the settings...

I changed the forum permissions so now anyone can read the Forum headings, however only registered users can read the posts.

I can also change it so anyone can read the posts, but only registered users can add posts.

I can make all these changes on a forum by forum basis. So I can make certain forums hidden to non registered users, such as Idea Parking Lot.

Plus I created a Guest Book that anyone can use to drop by and post something.