Has your friend checked that the two cards have the same amount of V/mem?? I have read that both cards must have similar memory moduals to work. In other words don't mix 1gb card with 2gb card. Also that mother board supports both Sli and Crossfire, it may have to be activated in the bios. Get him to read his mother board manual for the way to do that.
Get him to download the latest Nvidia control panel, he may be working with an old version.
See attached thumbnail.
Also try this site for help: -
http://forums.nvidia.com/index.php?showforum=207