Unlock All Tracks
At the "Push Start" screen, hold L1 + L2 + R1 + R2. A sound should confirm entry. Hold Down and X while still holding L1 + L2 + R1 + R2. Another sound should confirm properly. Press start with all the buttons still held.
Unlock all Cars
Press and hold L1 + L2 + R1 + R2 at the title screen. A sound should confirm entry. Hold Up and triangle while still holding L1 + L2 + R1 + R2. Another sound should confirm properly. Press start with all the buttons still held.