It's simple really......James Earl Jones was the voice of Darth Vader, but he's also made a few other films (Conan is all I know). All this guy did was take these sound clips and put them over StarWars.
There's some swearing.
http://www.youtube.com/watch?v=6A0rwG39Jzk
Oh and this one is good as well....
http://www.youtube.com/watch?v=5blbv4WF ... ed&search=