I had the same problem with my ATI card. Look on the internet for a program called powerstrip, it is freely available. Use this to set up custom resolutions. and refresh rates. I could not get it to 50Hz (my plasma wont accept it) but run it at 75Hz (a multiple of 25 used on PAL for frames per second). Powerstrip will over rule any settings that Catalyst sets up. Takes a bit to get it all working correctly but it is worth it.