Server2003 (the server os in the XP family) has been used by some as a workstation and gameing os. The reason ppl would use it thusly is 2k3 has a faster tcp stack and better memory management. It also has a per processor runqueue scheduler, better for HT/smp systems by far. Too bad 2k3 is so expensive.
Hmmm, I'll have to try this!