Start game as usual. Prior to entering each of the following cheat-
codes, go to the main menu, go to the Statistics sub-menu, go back
again (pressing DELETE), and finally enter your desired cheat: 

gimmesomecircuits    - Unlock Circuits
gimmesomesprints     - Unlock Sprint Circuits
gimmesomedrag        - Unlock Drag Circuits
gimmeppablo          - Unlock Petey Pablo
gotcharobzombie      - Unlock Rob Zombie
havyamystikal        - Unlock Mystikal
needmylostprophets   - Unlock Lost Prophets
119focus             - Unlock Car
893neon              - Un1ock Car
899eclipse           - Unlock Car
371impreza           - Unlock Car
222lancer            - Unlock Car
922sentra            - Unlock Car
667tiburon           - Unlock Car
334mygolf            - Unlock Car
77peugeot            - Unlock Car
777rx7               - Unlock Car
350350z              - Unlock Car
111skyline           - Unlock Car
221miata             - Unlock Car
2000s2000            - Unlock Car
889civic             - Unlock Car
228supra             - Unlock Car
240240sx             - Unlock Car
342integra           - Unlock Car
239celica            - Un1ock Car
973rsx777            - Unlock Car
allmylvloneparts     - 
allmylvl2parts       - 
seemylvl2parts       - 
driftdriftbaby       - 
slidingwithstyle     - 
givemenismo          -