During the game press CAPS LOCK to pause the game, 
then type any of the following:
Code           Result 
---------------------
DJARUM       - Pass through mushrooms.
HECTOR       - 8 lives.
MORRISON     - Complete level.
NALA         - Invincible.
ICE BOX      - Curve gun.
NUKE EM      - Destroys all nearby mushrooms.
SNAPPLE      - Padlock.
SQUISH       - Machine Gun.
USMC         - Adds 5,000 bonus.