At the title screen, hold L1 + R1 and press Up, Left, Down, Right, Left, Right, Left, Right to unlock all bonuses. If you entered code correctly, the word "Yeah!" will be spoken.
Go to the options menu, go to "Change Name", and enter "XOPENSEZ" as a name.
Win all races in C3 career mode to unlock Custom Corvette mode.
Win all C5 career mode races to unlock the Route 66 Challenge.
When losing a race or getting into to a wreck, press Start. Select "Restart Race" and the race will begin again, not be count against you.
When a cop starts to chase you, try to speed as much as possible or take a shortcut. With the 1978 Corvette 25th Anniversary, the cops will catch up with you -- try your best to get away from. Note: This will only work when you race one on one.