I think dude pirated it...Bottom line is that service packs will not install on a cracked version. Even if you find a copy without the validation process (which is slowly vanishing...) it still won't install because it checks your key before extraction.
You would know if it's not. Go to control panel, system or hit windows key + pause|break and look at the number under registered to. A legal copy should have "OEM" in there somewhere.