WindowsXP does not understand "optimal" video refresh rates.
For DirectX, you can over-ride the default (60Hz) refresh by doing Start-Run-DXDIAG, then selecting the "More Help" tab and clicking on "Override". You can set one refresh rate for all Direct3D modes. So, if I have set mine for 100Hz, that is great for most of the resolutions that I use, up to 1280x1024, but at 1600x1200 or 1920x1440, my monitor loses sync because it can only handle those resolutions at lower refresh rates. This fix does not seem to work with some OpenGL games. RtCW may have its own setting (I saw it in a ReadMe somewhere).
The best solution seems to be PowerStrip
, which lets you set lock in custom refresh rates for every resolution.