The Auction House in Forza 2 has been unavailable for what looks like the last 2 weeks. No one is sure if this is temporary or permenant. For now, that makes the Car Broker achievement (buy or sell 10 cars in the auction house) is currently unachievable. That makes the max in Forza 2 980g/1000g.
Again, it is not clear if this is a permenant shutdown or a temporary glitch.