go to control panel, dispay, settings, advanced and if you have an ATI radeon card, go to smartgear there is an option there to enable fast writes. I believe that the process with a nividia card is similar, but since never had one i'm not sure. If u look around in the advanced display settings you will find it.
You will also have to enable fast writes in your bios - should be under advanced chipset setting or something similar.
Word of warning fast writes can seriously destabilse a system and if you do have a ATI radeon card then i would leave it off. Perfomance gains with it on are minimal. Fast writes allows the CPU to send data to the Graphics card without having to go through RAM.