Highlight "Quick Race" at the menu, then press Start(13), X. If you entered the code correctly, you will hear a sound. You will start on quick race, but can quit.
In order to unlock the extreme cars, you must travel 750km in their respective WRC counterpart. Additionally, successfully complete the Wales Rally GB on the expert difficulty setting to unlock your cars respective Extreme version.
After each 100km you travel, you will unlock an "evolution" of the car. There are five "evolution" cars in all.
Successfully complete the Wales Rally GB on the extreme difficulty setting in first place to unlock all cars, including the Extreme and Concept cars.
Finish first, second, or third in the Overall Driver's Standings (at the end of the 2003 WRC season) to unlock the second half of the season (Germany, Australia, Wales (GB), Corsica (France), San Remo (Italy), Catalunya (Spain) and Finland) for time trials and single rallies. The default rallies available are Monaco, Sweden, New Zealand, Acropolis (Greece), Cyprus, Turkey (new event last year), and Argentina.