At the Start menu, select Options, then Cheat and enter one or more of these codes.

Effect	Code
UNLOCK ALL LEVELS	RMTE
UNLOCK ALL CHARACTERS	CAST
UNLOCK ALL COSTUMES	WRDB
ONE SHOT KILLS	MNKY
UNLOCK ALL WEAPONS MULTIPLAYER	DKSD
UNLOCK ALL WEAPONS SINGLEPLAYER	GTSM
MAXIMUM MONEY	PWTR
INFINITE AMMO	GGTY

Note: you will be unable to save upon activation.