The following codes must be entered at the main menu:

Infinite Boost

L1, R2, L1, R2, Square, Select.

Naboo Kaadu Racers

L1, R1, L2, R2.

Space Freighter Arena

L1, R1, Select, Circle

Unlock Galaxy Circuit

If you qualify into the top three on all of the tracks in the game, the Galaxy Circuit will be opened.

Darth Vader and Mirror Mode

To race as Darth Vader finish the GALAXY challenge with a gold medal, and with Anakin Skywalker, Darth Vader should be available. At the same time a Mirror Mode should open up, because you've completed the Galaxy circuit