Select the "New Game" option at the main menu. Enter GREYTHERAT as saved game name. All levels, including the bonus levels, will be unlocked. Enter M1A2U3L4!? as a saved game name to unlock all levels up to Darth Maul.
Battle Royal mission:
Defeat Darth Maul in level 25 to unlock the Battle Royal mission, where you have to fight eight other Jedi Masters in the Saber Arena.
Additional versus mode characters:
Defeat a character in the Jedi Arena during game play to unlock him or her in versus mode.
Hint: Get Wookie to help you in Level 1
In the introduction to the first level you will see a Wookie resembling Chewbacca walk past Obi-Wan. When the level starts, turn around and walk back the way the Wookie walked. You will eventually see the Wookie standing beside a fire. Walk up to the Wookie and talk to him. The Wookie will now follow you and help you take out the Black Heth Thugs.
(Submitted by: JediMaster-T)
To get unlimited force power in jedi battle mode, while selecting a character push the white button, black button, the right trigger, then the left trigger.