I thought people had already known about this, but with all the flame threads about how dawnguard may never come out for pc/ps3, I'm not sure. When you're in Skyrim and go to the start menu > general stats > quest, which shows you how many quests and quest lines you have completed, it says "Dawnguard Quests Completed - 0". I play on pc, so I can't say the same for ps3, but obviously they must be preparing to release the dlc.