Right there with you. This is the first game I've ever purchased from Steam, and I have no clue how I'm supposed to get this DLC to install. Is this just a case of Steam posting the DLC as available before it's actually available for download, or what? I can see it listed on Steam, and I can see it listed under "Additional Content" in game, but I can't select it in game, and I can;t download it through Steam (that I can see.)