Interesting, I had a similar issue when I installed the Skrim HD full version texture pack (version 1.2). My game would hang on startup. I suspected memory issues, but inspection revealed I still had plenty of RAM free. Googling around, I couldn't find anyone with my specific problem. However, I came upon this thread, and realizing that I had recently added a [MapMenu] section in my Skyrim.ini file to tweak with the map, I decided to try to remove that on a hunch. This time, the game loaded up fine with the new textures. Go figure.