Floating cars:
Enter 210741974 MARTY as a name.

Small cars:
Enter 01041977 BIGJIM as a name.

Smashed cars:
Enter 25121975 PILOU as a name.

Jelly cars:
Enter 07121974 FERGUS as a name.

Flat cars:
Enter 21051975 PTITDAV as a name.

Stretched cars:
Enter Gonzales SPEEDY as a name.

Realistic physics:
Enter WHEEL REAL as a name.

Small cars with high-pitched commentary:
Enter no first name and PALACH as a last name.

Mitsubishi Lancer Evolution VI:
Select career mode and win the 1.6L FWD championship in V-Rally mode.

SEAT Cordoba Repsol:
Win the Pirelli Challenge in challenge mode.

Subaru Impreza 2000:
Select career mode and win the 2.0L 4WD championship in V-Rally mode.

Toyota Corolla V-Rally:
Set a record time in all circuits.

Reversed tracks:
There are four tracks in each country. Beat the record of a track to unlock the next one. Unlock all of them to access the four reversed tracks for that country.

Extra challenges:
Win the Michelin Challenge in challenge mode.

Car preview:
Hold C-stick Left or C-stick Right at the car selection screen to open either door. Hold C-stick Up at the car selection screen to open the hood. Hold C-stick Down at the car selection screen to open the trunk.

Hint: Africa: Shortcut:
On the normal (not reversed) Africa track with the railtrack, follow the track and turn right when you get to the rails. Follow it and you will end up by the checkpoint with about six seconds off the fastest time.