Cheat Mode
Enter the gopher symbols as your name to unlock an extra menu at the options screen.

Level Select
At the main menu, select "Start Game." Next at the "Enter your initials" screen press Down, Down, Down, Down, Right, Down, Down, Down, Down, Right, Down, Down, Down, Down, A. Then select "Start Game" again. You'll now be able to select any level by pressing Right or Left at the following screen.