Then whats a CPU? Nothing in your link said I was wrong.
XP home supports one socket, but as many cores as you can get in there. XP pro supports more then one, and as many as you can put in there.
Or based off your new post, I'll fix it.
With either a core 2duo or a core 2 quad processor xp is good.
with quadcore and above windows 7 will do just fine.
XP will run quads just fine. Even home.