It should be in your Age of Empires 3 folder in My Computer.
Local disc C -> Program Files -> Microsoft Games -> Age of Empries III -> Sound.
I checked my AoE III folder and the TAD soundtrack is a little under 10 megabytes. There are six songs in two folders: Strategy ("KOTH", "Revolootin" and "SomeOfAKind"), and Interface ("EndCredits_606b", "MainTitle" and "OpeningTrailer_531a"). You can find at least three or four of them on YouTube by searching their name. I don't know about the rest.