Unless you have applications that take advantage of 64-bit processing, all you'd really gain is potential driver and compatibility issues. I believe that the 32-bit and 64-bit versions of Vista are not on the same DVD (though all editions, Home Basic through Ultimate, are). When I downloaded Vista from MSDN, there were separate 32-bit and 64-bit .iso files. I could be wrong, they may have packaged it differently for retail sale. Why? From my experience, Vista is just like XP, except prettier. I just tried it, and it runs. I didn't bother configuring it, but I would suppose everything works until someone shows otherwise.