In the main menu type : NUMBERONEDACRESTREET

It should bring up a menu displaying the cheats. Turn the ones on that you want.

During the game if you turned the cheats on you can turn them on or off by pressing :

F2 - easy shoot

F3 - invulnerability

F4 - infinite lives

F5 - infinite weapons

F6 - smart bomb

F7 - quit

F8 - stores current situation

F9 - reloads stored situation

F10 - frame wait on/off

F11 - restart