Secret Background:
     In  the  1st  level of the game, go to the conveyor belt and kill
the droid riding it and then you'll see a nice colored background

Radar:
     Pause  the  game and press Up, Down, Up, L, R, L. Yoda will laugh
and you will get radar that shows where hostages and enemies are.

Return to Last Checkpoint:
     To  return  to the last checkpoint you past after losing all your
lives  continue the game on the same level, pause, then press L, R, L,
L, R, R, L, R, R, L.

Jedi Power Battle Mode:
     During  a  two  player  game  press R, A, B, X, Y all at the same
time.  The  phrase  "Jedi  Power  Battles  On"  should appear and both
players can fight each other.

Unlock Bonus Characters:

Unlock Ki-Adi-Mundi: 
     Complete all seven training levels successfully in one session to
unlcok Ki-Adi-Mundi.

Unlock Captain Panaka: 
     Beat the game with Obi-Wan Kenobi.

Unlock the Battle Droid: 
     Beat the game with Mace Windu.

Unlock Darth Maul: 
     Beat the game with Qui Gon Jinn.