Non-vB login page

[Reevo]

Hi all

I'm in the process of developing a content management system that, when finished, will run 4+ sites. Some of these sites will have vB, but not all, and I'm looking for a way to cross-reference my members database with the vB one to such an extent that when the visitor registers on the website, it'll also register them for vB, and when they log into/out of the website, they're also logged into/out of vB.

I'm pretty keen not to hack around with the code of vB as I want future updates to be as painless as possible, so one solution I'd considered was creating a session var with the same login info & name as the one vB uses. My question is: has anyone done anything like this before, or has any tips for me before I start? Thought it'd be worth asking here first to attempt to save a few days bashing my head against a brick wall

Thanks