database linking and table linking

[patriotcow]

Ok I have this task that I want to do for 2 of my forums and maybe more in the future.
I would like to link tables from databases that are in seperate databases from each other.

E.g:

I have a database named vbulletin1 and in vbulletin1 there is a table called vb_users. Then I have a database named vbulletin2 and there is a table called vb_users. How would I link the 2 vb_users together so that on both forums the users are updated on both if you get me?

Thanks