What worked for me with my GTX 260 was to create a reg file and add this:
REGEDIT4
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Video\{BBB725CF-F867-4CFC-A00D-09A82F11A075}\0000]
"OverrideEdidFlags0"=hex:1E,6D,3F,56,00,00,FF,FF,04,00,00,00,7E,01,00
.
This works for me with vista but not in the Windows 7 beta. The driver fix wasn't giving me any luck there either.
Has anyone had this problem and found a fix?