This is just a re-upload of other peoples work for the sake of convenience.

Mount or Burn img
apply updates
extract dawnguard files and paste in Data directory of install location
play


If Dawnguard is giving you a problem try these steps by  elockloran

1. install update 9
2. install patch 7
(http://filesbb.com/lz59ob31k33z)
3. copy the extracted two dawnguard files (dawnguard.bsa and dawnguard.esm) to the Data folder in your skyrim install folder.
(my game is installed to E:GamesSkyrim so the 2 files needed to be dropped in E:GamesSkyrimData)
4. At the Skyrim Launcher, go into Data Files and check the Dawnguard.esm option to Load. If Data Files is greyed out follow steps 5 and 6.
5. Locate or search for the SkyrimPrefs.ini file that should be under your My Games subfolder. For example, mine is located at:
C:UsersELOCKLORANMy DocumentsMy GamesSkyrim
6. Open that file and search for [Launcher] and add "bEnableFileSelection=1". It'll look something like this:
[Launcher]
bShowAllResolutions=0
uLastAspectRatio=2
So add that line so it looks like:
[Launcher]
bShowAllResolutions=0
uLastAspectRatio=2
bEnableFileSelection=1
Now the Data Files option will be un-greyed and selectable. Follow step 4.
7. Launch the game and go talk to any generic Skyrim Guard. They'll give you a new quest item, Dawnguard, and you'll get the screen popup of new quest added.
This is how it worked for me. Some people won't have that greyed-out Data Files problem in steps 5-6, and it sounds like some people don't need to talk to a guard but get the Dawnguard quest automatically. YMMV.


Once again I am just uploading this for convenience I did not do the work behind this.  Hope it helps>