I rember there being this code for gt2 that let you buy any car at Tommy Karia's dealership. Is there some thing like this? Also, can you tell me the mastercode for these codes and the Lamborghini and Porche codes? Thanks guys.
Your best bet would be to look into Mk's Garage Editor. First you need to be able to transfer your save onto your computer, whether with a sharkport/X-port or through a cheat device like Gameshark/Codebreaker/Action Replay. Then follow the instructions to the Garage Editor, and open the your garage, and pick the cars you want.
GT3 is such an old game that most of the cheat codes are not too easy to find.