Use the following steps to enable Coolbits:
Step 1. Click on your Start Menu in the Windows Task Bar and select Run. When the command box opens, type "regedit" (without the quotes) and press OK. With the registry editor open (shown below), go to HKEY_LOCAL_MACHINE \SOFTWARE \NVIDIA Corporation \Global \NVTweak (expand the menu using the "+" expansion buttons to locate this menu item). Click on "NVTweak" in the menu. Next, right-click on the empty space inside right window and choose "New>DWORD value". Name the value "Coolbits" (without the quotes).
Step 2. Within the Registry Editor, right click on Coolbits and choose Modify. Change the Value data to "18" (without the quotes) and click OK. Exit the Registry Editor.
To get all of the Coolbits* SLI functionality, set Coolbits to 18.
To get all of the Coolbits SLI functionality AND Overclocking, set Coolbits to 1A.
For others out there who haven't used Coolbits before, simply follow these instructions to setup Coolbits:
http://www.slizone.com/object/slizone_appprofile_howto1.html
In Step 2 of the instructions, instead of setting Coolbits to 8, set the value to either 18 or 1A depending on whether or not you want to overclock your cards. Remember that overclocking voids manufacturer's warrantees, so do so at your own risk!
Remember when you do things in the registry you have to do them exactly in order for it to work. I followed these insructions and it worked for me.