Unlike the later Horizon games with licensed pop/rock radio stations, the first Forza Motorsport featured a mostly composed specifically for the game, plus a few licensed electronic tracks for menus and loading screens.
It sounds like you're looking for the track listing for the original (2005) on the original Xbox.
Here is the accurate content for the soundtrack. Forza Motorsport (2005) Original Soundtrack Composers: Junkie XL (Tom Holkenborg), BT (Brian Transeau), and various electronic artists.