While at the Enigma Machine, type in BALLOWAX.  The code can be enabled or disabled by selecting the bonus option beneath the machine.

Bullet Shield Mode

Pause the game and press B, B, R, L, Y, X.

Invincibility

Pause the game and press B, L, B, R, Y, L, X, Down.

Rubber Grenade Mode

While at the Enigma Machine, type in BOUNCE.  The code can be enabled or disabled by selecting the bonus option beneath the machine.

Silver Bullet Mode

While at the Enigma Machine, type in SILVERSHOT.  The code can be enabled or disabled by selecting the bonus option beneath the machine.

Sniper-O-Rama Mode

While at the Enigma Machine, type in SUPERSHOT.  The code can be enabled or disabled by selecting the bonus option beneath the machine.