Can't run 1920x1440 even though hardware supported

[koei]

I am running FC4 with Nvidia 6200 PCIe and ViewSonic PF795. Even though both the video card and the monitor supports 1920x1440. I cannot run it at "millions of colors" color depth. I am only allowed to select that resolution if I lower the color depth. I also installed the latest Nvidia linux driver for the video card but that didn't make any difference. Are there any ways of getting around this?

[koei]

Any input is appreciated