How do I get access to higher performance cars in multiplayer on Forza 3?

Question

When I enter races on xbox live all the other players tend to have access to higher performance cars. I know that tuning may have something to do with it, but many of the cars are accessible to me, and I don't think its just DLC cars.

Any suggestions?

Answer 1

Some of the cars are from a limited edition copy of the game, but it looks like the other ones get unlocked when you load the second disk.