Ace mode:
Highlight the "Hard" selection on the difficulty selection screen. Hold L1 + R1 until it changes to "Ace".

All licenses:
Successfully complete the Toyota Pod Event.

Extra credits for Gran Turismo 3 A-spec:
Complete 50% of the races to unlock a saved game file with 1,000,000,000 credits for Gran Turismo 3 A-spec.

Bonus FMV sequences:
Complete 100% of the races to unlock two FMV sequences