AMD[support.amd.com]
NVIDIA[www.nvidia.com]
Intel HD[downloadcenter.intel.com]

Video Mode --> set your native monitor resolution lowering to 1280x720 may help increase fps
Anti-Aliasing --> turn this off on older machines
Sync Every Fame --> turn this bad boy off unless you have massive screen tearing
Texture Filtering --> lower this on older machines
Anisotropic Filtering --> lower this on older machines
Texture Quality --> lower it based on your total VRAM
Shadows --> turn this off unless you have a powerful rig
Bullet Impacts --> doesn't affect performance unless your PC is very old
Number of Corpses --> lower it based on your total VRAM

Go to Steam>steamapps>common>call of duty black ops>players>config or config_mp

Modify config for SP/Zombies, config_mp for MP. Use CTRL+F to search commands.
If you want to change FOV in SP/Zombies you'll have to bind the following into your config file:
bind KEY "cg_fov NUMBER"
Example > bind P "cg_fov 80". Keep in mind increasing the FOV over 80 some animations/models might break resulting into your visual displeasure :P
DOES NOT WORK IN ZOMBIES ONLINE!

Question: Can I get banned for the modifications above?
Answer: Not at all. These are all client side modifications that only affect you.

Question: Help! My game is crashing/doesn't launch/black screen. What do?
Answer: I have mentioned above to create a backup! Delete both config files in the players folder, this will make all your settings reset to default.

Question: I'm getting worse performance than before. Hello?
Answer: If you were following my instructions step by step you would not be on the negative. You messed up somewhere, replace/delete your config files.