That's what I thought first; but monitor should be plug and play. No drivers on Chimei website.
The manual of the CMV223D monitor says:
Video chips below support the resolution 1680x1050:
Geforce4 Ti4200 , Geforce PCX6200 ,
ATI Radeon 9600 , ATI RadeonRX300
Matrox P750 , Nvidia Geforce2 , I865G , I915G
So looks like 1680x1050 is not supported on a ATIRadeon9200.
I noticed there is more people with this problem.... e.g. http://forums.nvidia.com/index.php?showtopic=85838