OpenGL Error

[Grole]

I can't seem to run a few different games because of this error:

...WARNING: could not set the given mode (4)
...setting mode 4: 800 600 FS
...using colorsbits of 16
...calling CDS: ok
...created window@0,0 (800x600)
Initializing OpenGL driver
...getting DC: succeeded
...GLW_ChoosePFD( 16, 16, 0 )
...35 PFDs found
...GLW_ChoosePFD failed
...failed to find an appropriate PIXELFORMAT
...restoring display settings
...WARNING: could not set the given mode (3)
...shutting down QGL
...unloading OpenGL DLL
----- CL_Shutdown -----
RE_Shutdown( 1 )
-----------------------
Hunk_Clear: reset the hunk ok
GLW_StartOpenGL() - could not load OpenGL subsystem

I've gotten this message of a few games. This I got when I tried to run the Call of Duty Demo, but I've had it before when trying to run Medal Of Honour (full version). This is frustrating because I was able to run it before on this machine when I had Windows 2000 on it.

Currently I'm running XP Pro, fully updated and directX 9.0b. My computer is an Intel PIII 866, 192mb, 32mb ATI Radeon video Card. I have not changed the hardware since I first ran the game with 2k.

Can anyone tell me why I'm getting this error, and what I can do about it?

Thanks