Pretty much all of them run on XP (and vista I think) by now. Just get the one of the new sourceports (like the Doomsday Engine, supports Doom, Heretic, Hexen). Gameplay is unchanged, but with 3D-Support incl. higher resolution and dynamic lighting, in-game setups, quake-style console for all, mouselook etc etc etc.... At least all ID games up to Q2 have been released by id Software and fully refurbished by fans... Highly recommended...