I've begun to implement this sort to use vB as the guestbook system for our users. All I've done (works, but not debugged fully yet) is hack the files that create a forum to pass the users parameter and created a new version of the files for creating and displaying new threads so that they use a different template. The one thing I still want to do is make that user the moderator and assign priveliges, however, vB has a pretty funky users and groups setup that I haven't wanted to dig into. Also, I am still investigating where in the database to keep some of this info.
I'll keep you all updated once I get back on it.