You can download a free 180-day trial of WinXP Pro x64 Edition from Microsoft's website if you want to try it for yourself. My experience was basically "install WinXP Pro x64, install HalfLife2 and FarCry, play 'til my eyeballs fall out." Worked fine. Now, trying to hitch up a plethora of aftermarket hardware (scanners, printers, video-capture cards, etc) may run you up against lack of driver support. But you can try before you buy, if you'd like to.
*gropes around on floor for eyeballs*