On the title screen or during the intro, type "FLEV17" and press 'RETURN'. This will give you infinite lives. Use the function keys to skip levels. The screen will flash letting you know it worked.
For a bit of fun on the title screen or during the intro, type "I AM EXQUISITELY EVIL" and press 'RETURN'. This will change the names on the high score table and you can kill polar bears and people. The screen will flash letting you know it worked.