Once Gutsy Gibbon come out (sometime in early October) Ubuntu Studio will be available in 64bit. As of Gutsy Gibbon, all of the packages contained in Ubuntu Studio will be in the official Ubuntu repo, meaning all architectures supported!

At the moment Ubuntu Studio has its own repo for a few programs (ardour, wired) that didnt quite make the official repo in time for Fiesty

be sure to check out the ubuntu studio tutorial blog @ http://www.ubustu.com