Yes this is a trailer for new Skyrim content and it looks fantastic. There is definitely an emphasis on the undead with lots of vampires and zombies. From the voice-over it sounds as if you may be trying to enable vampires to live in the sun.
Looking closer at the trailer it appears you will either be a vampire or one of the Dawnguard, a Van Helsing type group. There will be different vampire beast forms, mounted combat and crossbows!
Oh and a Dragon seems to dive through some ice into a lake.
Called Dawnguard it is the first game add-on for Skyrim. Dawnguard will be available for download for 1600 Microsoft Points on Xbox LIVE this summer.
I imagine there will be an awful lot on this expansion pack.