On the one or two player select screen, type "SPICY BEANBURGER" (it's "KID" on another version. The guy should then jump up and down. During play, but not on the map screen, press: '=' to add guys. Press 'ENTER' on the keypad to get a card. When you get to the bonus room, if you fall down to the exit, then press 'Fire', it'll open. While it's open, press 'P' and you should be given another go at the bonus room.