The commands in cod are very very similar to quake3. You could probably find a decent webby specific to cod with a quick google .... but an excellent q3 config guide can be found here:
http://ucguides.savagehelp.com/Quake3/FPS_visuals.html
and should be very useful. It's particularly good at explaining framerates and helping you get your fps up and capping it and other settings at sensible levels.
The config files for cod can be found at
'C:\Program Files\Call of Duty\Main\config.cfg' for your single player (offline) config, and
'C:\Program Files\Call of Duty\Main\config_mp.cfg' for your multiplayer (online) config
compare some of the settings suggested on the link above to those in your config files and play about with them. Or you can try each command from within cod in the console. If you find a setting that works, use '/seta' followed by the command and value and it will write that setting to your config file for you.
cham