One User Database, Two Forums

[ShannonA]

I'm getting ready to roll-out a new vBulletin forum which will share some percentage of users with an old one. I'm trying to figure out if there's any way to do this elegantly, ideally by having shared user database resources between the two forums.

I'm aware of at least one partial OpenID solution, where users can create accounts on both boards, then access each of them with a joint OpenID login.

I'd prefer a method whereby both boards when to the same user database or else one board regularly synced its database to the other.

Is there anything out there?