I’m a software and network support/admin guy and IME Windows 2000 runs most games just fine, but these days, as long as you’ve got a reasonably modern PC (Pentium 2 or better and 256 MB) there is no reason not to run XP (Home or Pro). Memory is more important than processor speed at the low end, and memory is cheap.
If you’ve got an older computer, run Windows 98SE
2K and XP are vastly stabler than any earlier offering from MS. Absent hardware problems, my XP and 2K machines simply don’t crash