Extremely important task. <Creating vBulletin forums with same user database>

[SEOvB]

I've never seen this done before; it sounds like you'll need custom code, and a lot of it. Just exporting and importing the user table will only get you so far. You'll need to either automate this process or establish a system that will keep the user table of all the vB forums in sync.

Probably the easiest way to do this would be to add a plugin to each forum that would auto-register the user to all forums when they register on the one. Still, that will only keep the login info in sync, and only if the user never changes his password. If you want post counts or other user info (like custom profile fields) synced up as well, you're going to need even more custom coding.

I assume you have 4 vB licenses ready to go? If so, I'd look in the paid modification forum.

-Nick, SEOvB Developer