Media Temple // Shared User Database

I’m currently running 2.6 on Media Temple’s GS service. (I’m very happy with them as a host, so I don’t need recommendations to move or switch).

I really only have one website up and running right now that has a significant user base. But the intention is to start building other sites that would branch off from that main one (similar content, all comics based). I’m wondering if anyone knows how I might set up the wordpress install to use the existing user database instead of creating it’s own? The new sites are in seperate domain folders, but the database is all running off the same MySQL.

I’m half decent with PHP (I can follow instructions, :)) But when it comes to database stuff, I’m a bull in a China shop. Any resources or ideas you might have on making this work would be appreciated.