Microsoft Windows XP End User Licence Agreement
I just saw this when I was reading the Windows XP EULA:
The software may not be used by more than two (2) processors at any one time on any single workstation computer.
That seems to suggest that MS won’t let you install XP on a machine with more than two processors. I don’t know what that means for Intel’s new Core Duo line of processors. If you had two Core Duos in a machine, looks like you have to run some form of *nix. Not that that’s a bad thing.