I had the “could not open glsubsystem” message as well. I happen to be using an HDTV as a monitor at the moment, which has a max resolution of 800x600, while the demo was attempting to run at 1024x768. The hint was in the message:
----- R_Init -----
Initializing OpenGL subsystem
…initializing QGL
…calling LoadLibrary( ‘C:\WINDOWS\System32\opengl32.dll’ ): succeeded
…setting mode 6: 1024 768 FS
…using colorsbits of 32
…calling CDS: failed, bad mode
…trying next higher resolution: failed, bad mode
…restoring display settings
After a fruitless search for a command line parameter (everyone’s interested in how to cheat…) I broke down and opened up the .pk3 files for a look, and found the answer in the safemode.cfg file. By adding +set r_mode 3 to the command line, I was able to get CoD started in 640x480 mode and adjust the resolution from there.
Some other parameters from the safemode.cfg:
set r_mode 3
set r_fullscreen 1
set r_colorbits 32
So, try a different render mode, or turn fullscreen off initially (set it to 0), or try 16 bit color. Hope it helps.