Enter "SEMPRINI" into the high score table. A couple of new options will then appear on the main options page. The first will allow you to select and start on any level up to the highest one you reached, and the second option will allow you to show/hide the hidden bonuses.
Enter your name in as "POOKY". Now when you next view the high scores it will change to "NO IT ISN'T!". I think this is a joke from the programmer who was also responsible for the Rick Dangerous games.