"Profile import is, among other things, our way of rewarding long-time Forza Motorsport players. How does the system work?
It’s all automatic. After your first race (logged in with the same Xbox Profile you played Forza Motorsport 3 with), you will be asked if you want to import your profile. This will have no effect of your Forza 3 profile. It’s just a read on that profile. The import process looks at several factors and gives a variety of rewards. If you’re connected to the server and your Xbox LIVE account is in good standing, you will be gifted credits based on your level. The car imports do not require connection to LIVE."