Unlock Anakin (Episode 1):

Get the fastest lap time on every track.

Darth Maul:

Get the top KO score on every track.

Watto:

Get in the fastest three lap times for every track.

Darth Vader:

Unlock Anakin (Episode 1), Watto, and Darth Maul, then win Tournament mode

as one of them.

Unlock Episode One Sebulba:

Beat the game with Sebulba.

Unlcok the all Three Art Galleries:

Beat all 13 races in tournament mode.

GameShark Codes

Unlock Darth Vader and Darth Maul
(M) Master Code Must Be On
0E3C7DF21853E59E
EEAF17C6BCDACE32

Unlock Vader
CE5D3F3ABCA99B84

Unlock Maul
CE5D3F2EBCA99B84

Thanks to Revolution reader Travis, kc, Litarvan13 and Grimlok!