You'll need an online PSN connection for this exploit. Create a NEW account and sign into the PlayStation Network. When you set up your account, set up your birth date for the current calendar date. You will be awarded a car on the MM/DD of your "birthday," and the year actually determines what sort of car you will get (so set it to whatever year you want a random car from). Enter GT Mode to receive your online B-day reward/coupon for your free car. Give the free car to your actual account as a gift. You can repeat this endlessly for free cars!