You need to download a tool called "coolbits". Here's what to do. Download the latest nVidia drivers from their site
here. Then you will need to download the coolbits registry tweak
here. Now that you've got that, all you need are instructions. What better place to get them than
here!? Once you properly enter coolbits into your registry, a new tab will be unlocked in your nVidia control panel, allowing you to oc with ease

Enjoy