A very basic MySQL set-up question for the database aces out there.

I'm planning to set up a VBulletin forum on recently acquired PHP server space.

It is intended that the messages submitted will be stored on an expandable database from which subscribers can access and view the threads by entering 1)key subject words or 2)the username or 3)date thread was submitted, etc.

Also required will be the registration details (protected) of the subscribers.

Essentially, what I'd like to know is will I need two databases (one for the threads; and 1 for the subscribers) or just the one?

Your word on this and start-up would be much appreciated.