Solstheim is a county of Morrowind, and that is where you'll fight your new nemesis. Bethesda has been mum on the details containing Morrowind but more will be known in time.
The add-on will be released December 6 for the Xbox 360 and will cost 1600 Microsoft Points. PC and PS3 release dates have yet to be announced and as far as Bethesda and Sony are concerned...this might not hit PS3 (just like the other DLC).