On the high score screen, type "SKID ROW". I'm not sure this does anything other than put "18 and life" as your name on the high score table. At any time, type "QUIDITY" and use the 'Space' bar to skip levels; the 'Help' key to toggle infinite lives; 'F4' to switch to NTSC video mode; and 'F5' to switch to PAL video mode. If the game ends or you reset the game by pressing 'F1', you'll have to enter the code again.