The price/performance ratio on a Mac Pro WRT. gaming is pretty low, but it's Quad Conroe/1,3Ghz bus with darn good graphics (X1900XT, not the 7300 which is only decent) so it'll definitely fly.
It is (close to) impossible to install Win XP prior to SP2 due to the lack of built-in SATA drivers (and a floppy drive in the mac for driver disks). It MAY be possible to load the driver onto an USB stick though, but that's just a thought, I haven't tried nor seen it documented (or looked even).
Here's how to slipstream:
http://maximumpc.com/2005/01/how_to_slipstre.html