[otlayi]

I fought with the same thing for a while, eventually giving in and writing a system that uses vB's global.php to achieve the best results. There are a few functions that vB uses to handle logins and sessions, you can for-sure make your site read from and check vB's user database, no problem, but then you're not logged into vB as well. It's nice to have your site and forums be traversable back and forth while keeping you logged in, and also trying to just patch into a little bit of vB's code is next to a nightmare unless you've got a lot of time on your hands to extensively dig through their code to figure out all the small pieces that they're doing onlogin.