If you have a save file from GT3 you can import money and licenses into GT4. You can transfer license qualifications but you do not receive the unlockable items that come with the license when you get them without importing. You can transfer money up to 100,000 dollars. This can only be done once.
Best Starting Car
To smoke the competition at the beginning of the game purchase the Mitsubishi Lancer Evolution GSR '92, on sale in the Used Car Showroom I.
When you buy or receive a new car, before driving it change the oil. This will increase the Horse Power of the car, which sometimes can be a pretty significant increase.
Start out with any vehicle you like. When you make enough money to make your vehicle faster using the beginner hall, move over the the special conditions Hall. Defeat the first race Rally d' Umbria and you will receive a Cadillac CIEN '02. Get more money and put more power into your Cadillac CIEN '02 you won't have to if you don't want to. The CIEN will gain almost 1000 HP. Go to the second race with the CEIN in the Special Conditions Hall called Rally d' Capri. After you win that race you will get a Toyota RSC Rally Raid Car '02 which you can sell for more than 230,000. Keep racing that race and keep making the money.