If you have one of the newer retail boxed PII's then you will need a TorX T8 bit to remove the four screws that hold the P.O.S. heatsink onto the backplate. You can get one at a local hardware store or auto supply store that sells screwdrivers.
DO NOT try to use an Allen Hex Head wrench or you will strip the head and then you will have to drill out the screws.