I'm running Vista Ultimate 64bit on my new system and it runs flawlessly. And just for clarification, it's not MORE than 4 gigs, its even if you want to run 4 gigs period, you need to have 64 bit to utilize all of it. With my latest system, a 512MB video card, and everything else, my 32bit OS would only recognize 2.75GB out of my 4. So actually if you're running more than 3GB, you're better off with a 64 bit setup to utilize all of your RAM.