how to integrate with my current user account system?
 

My site has a custom login and registration system, and I'd like to add a forum onto it. I want to allow users to use the forum without creating a forum account separate from their regular account. I want to use my existing account system, that is, deactivate the forum's login/logout/registration, and have the forum identify who's logged in via existing session variables. I've not been able to find any info about how to do this. Is it easy enough to do with vbulletin, and is there documentation for how to do it?