Windows XP Pro Service Pack 2,I havent upgraded to Vista since i am afraid that the drivers compatibility are still buggy.I think ill upgrade somewhere next year where ill upgrade the specs.Right now i am running on a Pentium D 3.20Ghz , 2 GB of RAM. I am planning to instal a Core 2 Extreme, but i have to change the motherboard as well, since so far allows me the Pentium D.