To enable cheats you need to alter the shortcut to the CODSP.exe as follows:

Original shortcut target:
“C:\Program Files\Games\Call of Duty\CoDSP.exe”

New shortcut target:
“C:\Program Files\Games\Call of Duty\CoDSP.exe” +set thereisacow 1337 +set sv_cheats 1

After doing so cheats can be entered in the console (don’t forget to enable this in options).

god – godmode
give ammo – full ammo
notarget – ignored by enemies

Give ’em bloody hell. Yo ho!