Car Carry Over
An option is available in the "Prologue" version in which your "Prologue" save game actually can be integrated with the full release "Gran Turismo 4" save games. This means if you unlocked all the cars and completed all the tests in "Prologue" they will be available in the full game.
Bonus Car
An extra fast and powerful car is available to unlock in the School Mode. You must gain gold ratings in each of the sections. Once you have achieved these ratings, the car will be yours to race. This cheat can be used in all gaming modes and can even be integrated into the full "Gran Turismo 4" game. This makes the full game much easier.
License Test Cheats
You must earn new licenses regularly in "Gran Turismo 4 Prologue." These licenses unlock other cars and tracks. There is a simple way to pass many of these tests. Hold the R3 button while you perform the test. A line will appear that indicates where you are to drive, accelerate, stop and turn. Following this line exactly will let you pass the license test every time.