From the Options menu, select the option to enter codes and then enter 
the codes indicated below to unlock the corresponding vehicles.

TUN58396  - All Drift Cars.
MUS59279  - All Muscle Cars.
F93857372 - Buchbinder Emotional Engineering BMW 320si.
G29782655 - Gamestation BMW 320si.
M38572343 - Micromania Pagani Zonda R.
P47203845 - Play.com Aston Martn DBR-9.