Beat the game with Qui Gon. Then at the character screen highlight Qui Gon press select with X. You will be Darth Maul for the game.

Beat the game with Plo Koon. Then at the level select there will be an extra level with a droid on the front. You are that droid in the queen's palace.

Beat the game with jedi mode. (Diffuculty) At the end you have a level select called Gungun Round Up.