Instructions
Open "My Computer" or "Windows Explorer." Navigate to your "Call of Duty" directory. By default, it installs to "\Program Files\Activision\Call of Duty Black Ops." If you installed the game via Steam, you'll find the directory at "\Program Files\Steam\SteamApps\Common\Call of Duty Black Ops."
Right-click on the file "config.cfg" and select "Open With" and then "Notepad."
Hold down "CTRL" and then press "F." This opens the search box. Type "seta monkeytoy" into the box and then click "Next." This brings you to the seta monkeytoy entry. Next to it is a number.
Replace the number next to seta monkeytoy with "0" -- minus the quotation marks. Click "File" and then "Save." Exit the program.
Start "Call of Duty: Black Ops" and select a level to play. During gameplay, push the "~" key in the top left corner of your keyboard. This opens a command prompt. Type "/give ammo" in the command prompt, once again omitting the quotation marks. This fills your ammo up.
Use the "/give ammo" code as often as necessary to keep your ammo full.