To get the fastest racer in the game you must first unlock Anakin Skywalker (Episode 1), Darth Maul and Watto. Then using one of those characters you have to complete tournament mode to unlock the Lord of the Sith.
When you set a record (Best Lap, Best 3 Lap or Most KO's) and then enter 'NO TIME' as your name at the 'Name Entry' screen the 'Cheat' mode will become enabled allowing you to enter the following codes at the 'Main' menu unlocking the corresponding feature.
Unlock Hard Mode: At the 'Main' menu hold L1 + L2 + R1 + R2 and quickly press Triangle.
Unlock ALL Tracks: At the 'Main' menu hold L1 + L2 + R1 + R2 and quickly press Right, Left, Right, Left, Circle, Square, Circle, Square.
Unlock ALL Art Galleries: At the 'Main' menu hold L1 + L2 + R1 + R2 and quickly press Right, Square, Left, Circle, Down, X, Up, Triangle.