At the title screen, go to "Unlock" and then insert code. Try CAPS-LOCK if the codes don't seem to work.

Password	Effect
hujtre	Laser Cutter
ignblk	Black Suit for Napoleon and Ilya
igngun	Machine Gun
ignily	Spy Suit for Ily
igninv	Invincibility
ignroc	Rock Crawler
mkghys	Harbor Mission
prfvbh	Sport Car
zxdfrt	Infinite Ammo