Edit: Whoa, it looks like they encrypted it this time and you can't access it???
They haven't encrypted it. It uses XBOX XWM-Files instead of MP3s, and the game has regional music just like Fallout.
To add new songs (i.e. not replacing the old ones) you need to create a new "Media Set" with the song and add it to the "Media Location Controller" of each region where the song should play.
So we need an ESP to add new music. We might be able to edit the Skyrim media sets using FOMM/TESsnip and the Fallout3-GECK. If that doesn't work we need to wait for the CK
see here for XWM files:
http://www.gamesas.com/index.php?/topic/1262248-adding-your-own-music-to-the-game/page__view__findpost__p__19210527