Windows XP GENUINE OEM!!!! I actually paid for it when I built my system lol and I've only reformatted twice lol. I had a LEGAL beta of vista ultimate and hated it. So I stuck to xp pro and still am. I tried installing mac osx leopard (dont ask why, i now question myself why but its because i got bored and i was home for spring break) but that didnt work and its just too complicated trying to do it on an amd system. so here I am, on xp pro.