I'm one prime cantidate for anti-OCing. I used to OC everything I had, but recently I just broke my video card doing it and well I've learned my lesson. You don't get any noticeable gains at all, just shortens the life of your stuff and voids warranties, etc.
But if you really want to, the easiest way is to install Coolbits. Do this my going into regedit, HKEY_LOCAL_MACHINE, SOFTWARE, NVIDIA Corp, Global, NVTweak. In the NVTweak folder, rightclick, new -> DWORD Value. Call it Coolbits. The right click it, Modify, set Value Data to 3, close out of regedit and reboot. In your NVidia display settings, there will be a new tab for clock frequency and such.
But again, I urge you not to OC your video card, it's very expensive and can break quite easily.