Enter G0LVL G'zero'LVL followed by the level you want to start at. Now ACCEPT. The message "Cheat Activated=" appears and select Quit. Then start a new game. Now you will start at the level you want. The levels go up to 34 and 35 is the ending cinema.
Access All Weapons All Levels Invincibility and Unlimited Firepower
Enter 1GOTP1NK8C1DBOOTSON at the password screen. The message "Cheats Enabled" will appear if done correctly.