You’re able to buy the DLC for 1600 Microsoft points.
With this this official add-on for The Elder Scrolls V: Skyrim, journey off the coast of Morrowind, to the island of Solstheim. Encounter new towns, dungeons, and quests, as you traverse the ash wastes and glacial valleys of this new land. Become more powerful with new shouts that bend the will of your enemies and even tame dragons. Your fate, and the fate of Solstheim, hangs in the balance as you face off against your deadliest adversary – the first Dragonborn.
In related news to this, the DLC will also be available for PC and PS3 in early 2013. The question is if Bethesda will have the same amount of issues with the PS3 release as they had with the Dawnguard DLC.