Look for Coolbits to unlock nvidia's OC feature. It's actually a registry tweak:
To enable the Coolbits tweak open REGEDIT (start\run then type regedit) and navigate to HKEY_LOCAL_MACHINE\Software\NVIDIA Corporation\Global\NVTweak.
If the Coolbits value is already present in the right hand pane, double click on it and change its value to 3. If not, Right click in an empty area of the right hand pane and choose new\dword value. Call the new value Coolbits and give it a value of 3.
Close REGEDIT. Now when the nVidia display control panel is opened, there is a new clock frequency page.
Rivatuner can help you unlock some pipes in your video card:
There are other good programs on there too.