Is this Idea Possible.
 

I want to run 5 domains, 5 different sites.

I want each to have vBulletin forums built in it.

I want to make a 'network' which requires only one account to be registered to then be able to access all parts of these domains.

Though each site has its own style, and separate forum look, and have Forums/sub forums to its specifics.

For Example. One site will talk about cars another will talk about books. Two different websites, from the domain, and you can click a link from the navbar or so to visit either pages, and still have the same account.

Essentially making one account to access all sites, if you visited.

Is this possible?

(sorry I am a website newbie, who has a stretched concept)