It's just a registry hack. It enables a few features that's normally hidden in the nVidia control panel, including VSYNC control for D3D and an overclocking slider. Copy/paste the following into a text file with Notepad:
REGEDIT4
[HKEY_LOCAL_MACHINE\SOFTWARE\NVIDIA Corporation\Global\NVTweak]
"CoolBits"=dword:00000003
Name it something with the .reg extension (ie. coolbits.reg). Double-click to install and you should see the extra tab when you next open up your nVidia control panel.