Ya know I did just that (XP 64bit) just 2 days ago. Man it was nasty. Seemed alot slower than regular XP and wasn't customizable at all. Plus there was alot of wasted space time and resources with the 32 bit subsystem stuff they have in it. (Just to keep compatability with everything out there) Didn't work out well. If you got the time and the need you can get a trial of XP 64 bit and try for yourself but as my 2 cents go its in the trash bin of my mind now ... I really have disliked vista but after getting this rig and trying a pre-integrated version of SP1 (I have an MSDN account) it seems like SP1 just MIGHT make vista worth it. So I would wait untill you can get SP1 final preintegrated disks for retail untill you go for vista.