Sadly, there is a 64 bit XP and a 64 bit Win 2003 out there. But, as Erlik mentioned, not many drivers. A coworker just rebuilt his home system: dual core top of the line Athlon 64 bit, high end drives, motherboard, top of the line Nvidia card, etc. He was able to get his $150+ logitech eyeball cam working, printer, scanner, etc. All was fine...except that 1 application didn't work under 64 bit, the virtual private network (VPN) software required to connect to our employer's network. Thankfully he doesn't need to do it often and has 5+ other machines he could use. Until Vista is out and you have 'new' hardware that manufacturers readily support and write 64bit drivers for you may have problems. Side problem: you can not readily buy the 64 bit XP at a store. Microsoft is not selling it in boxed form and don't intend to. You can turn in your 32 bit license for a 64 bit license (1 direction only, no give backs) from Microsoft and possibly your hardware vendor if you bought from say, Dell. So, unless you are ready to save all your info on your hard drive, turn in your license, reformat to 64 bit and hope to hell it all works...I wouldn't recommend it. Yea, I know, sad. If I could get a true 64 bit OS (Windows, sorry) with full software support and hardware support I would upgrade my hardware and get the 64bit...but since I can't, I'll just wait a year to build a new system with Vista and new hardware then.