To clear up confusion... The 2.4 gb update was this track alone. It really is that big and detailed, along with finally having the elevation changes the track actually has (if i remember right its a couple thousand feet of elevation changes start to finish) You select the track in the free play section, and if your curious you do level and get credits for doing so. I'm not aware if its in career or not, I have heard its not tho :-(
Anyways its the most fun track on the game imo, I'm running it back to back to back since yeterday in my F40. Its nice to finally race this track with a real scan. It was good in old forzas but felt very flat for what the track is. Between this track and halo 2 alone, yesterday was a great day.