Win the indicated event in first place to unlock the corresponding car.

Colin McRae Challenge: 1995 Subaru Impreza WRX STi with chrome Colin McRae livery.
World Tour: Rally Cross: Ford RS200 Evolution.
World Tour: Landrush: Toyota Stadium Truck.
World Tour: Raid: Mitsubishi Pajero Dakar 1993.
World Tour: Trailblazer: Dallenbach Special.
X-Games: Europe: Colin McRae R4 with X-Games livery; Rallycross only.
X-Games: Asia: Mitsubishi Lancer Evolution with X-Games livery; Trailblazer only.
X-Games: North America: Subaru Impreza WRX STi with X-Games livery; Rally only.
X-Games: All completed: Ford Escort MKII and MG Metro 6R4.

Have a saved game file from the original DiRT to unlock the Subaru Impreza STi Group N with No Fear (Gold) livery.
Have a saved game file from Grid to unlock the Subaru Impreza STi Group N with Ravenwest livery.