CPU: quad-core Intel/AMD
VGA: DX9 video card with 1 GB GTX 260/Radeon 4890 or higher
OS: Win XP/ 7
Sound: DX compatible sound card
Network: Internet Access for Steam activation
This is the Dawnguard DLC pure, plain, and simple, with no installers, and no cracks. It will work on a properly cracked Skyrim game updated to the latest version (currently 220.127.116.11.8, aka Update 13). It will also work with the bought version from Steam.
This is a 7-zip file properly compressed. To install, simply extract Dawnguard.esm and Dawnguard.bsa into the Data directory of your Skyrim installation and check it in the Skyrim Launcher. Or, if you prefer, you may simply import it into your favorite mod manager (Nexus Mod Manager, for instance), and it will install it for you.
As always, if you like the game, BUY IT. Support good game developers!