Not all users will have access to all of Forza 3 due to multiple DVDs.

[Undying]

dougsdad0629 said:

But the 360’s basic Arcade SKU, of course, doesn’t come with a hard drive; a near-certain indication that 360 Arcade owners will not be able to play the full game.

Well thats what you get for buying the "tard pack", to steal a term from Shane Bettenhausen.