All vehicles and tracks
First go to the options screen [hold square and press up, circle, down, circle, left, right, left, right, circle]. This will open a new menu called "secret menu". Don't go there yet. Now for the second part -> start a single player game and type in NORTHEND as your name. This will open another menu under secret called "Top secret" where you can turn all vehicles on/off. So back out and go into options and you're set.
All vehicles and tracks ( Japanese version )
At the Main-Menu select ''Options''. Now at the Options screen press and hold SQUARE, then press UP, TRIANGLE, DOWN, TRIANGLE, LEFT, RIGHT, LEFT, RIGHT, TRIANGLE. If you entered the code correctly you will see the bar ''SECRET'' below ''Reset Options'' in the Options-Menu. Now return to the Main-Menu, select Single Player, and then enter ''NORTHEND'' as a name. If you entered the code correctly, a voice will say, ''Wild Wild Racing!'' Return to the Main-Menu, select Options, then select ''SECRET''. At the Secrets screen, select ''TOP SECRET''. There you can turn on to have all cars, all upgrades, etc.
All vehicles and tracks...