At the 'Driver DNA Lab' option highlight 'Celebrity Face Off' and beat the character on ALL 3 of their races to unlock the corresponding car.

Unock Audi 1.8T Quattro:
Beat Caballero in ALL 3 of his race challenges.

Unock Nissan Skyline R32 GTS-t Type M:
Beat Tarzan Yamada in ALL 3 of his race challenges.

Unock Dodge Viper SRT-10:
Beat Samuel Hubinette in ALL 3 of his race challenges.

Unock Ford Mustang Fastback:
Beat Djibril Cisse in ALL 3 of his race challenges.

Unock Nissan Silvia S15 Spec-R:
Beat Phil Morrison in ALL 3 of his race challenges.

Unock Toyota Corolla GT-S:
Beat Beau Yates in ALL 3 of his race challenges.

Unock Ford Mustang GT '05:
Beat Smudo in ALL 3 of his race challenges.

To get the following customised DNA lab cars you must first enter the code which unlocks a special challenge which you must beat to get the car

Unlock Ascari KZ1:
Enter the code KNOX

Unlock Audi TT 1.8 Quattro:
Enter the code YTHZ

Unlock BMW Z4 Roadster:
Enter the code GVDL

Unlock Holden Monaro:
Enter the code RBSG

Unlock Hyundi Coupe 2.7 V6:
Enter the code BSLU

Unlock Infinity G35:
Enter the code MRHC

Unlock Infinity G35 (Red Design):
Enter the code MNCH

Unlock Koenigsegg CCX:
Enter the code KDTR

Unlock Mitsubishi Prototype X:
Enter the code DOPX

Unlock Nissan 350Z:
Enter the code PRGN

Unlock Nissan Skyline R34 GT-R:
Enter the code JWRS

Unlock Saleen S7:
Enter the code WIKF

Unlock Seat Leon Cupra R:
Enter the code FAMQ