Hmm, if your mate has the same system set up and he/she is not getting any problems then have a look at his system set up and see how it's running. Have a look at the drivers he/she is running, the Power supply strength and cooling.
That's all I can think of...90% of the time it's the easiest thing.
*Edit... If you're still not sure -
1- If you're sure it's not a driver issue then try these....
2- Start by looking at cooling, cooling the case better rather than the card directly could help. If the air coming out feels quite warm on your hand then the chances are there is not enough air going in and then out of the case, regardless if it's a cool room or enough space for your system. A couple of cheap fans one on the front blowing in and one on the back bowing out could make all the difference. (Fans at front should blow in from bottom of case as hot air rises - then fans at back of case usually about half way up will expell extra hot air).
3- There is a remote chance that it's a power supply issue... the card might simply not be getting enough juice so see what Power supply your mate is running with his comapred to yours. In the instructions of your video card it should say what the recommended power supply should be (PSU).
Other than these I'm pretty stumped...
Good to see this site is still going 
