Oops, no. Sorry. You'd either need the master tapes for that (good luck!) or a copy of the movie soundtracks and/or something like "The Story of Star Wars" for dialogue.
Believe me, I've tried to isolate dialogue/effects for various reasons, and it always sounds like crap.
That being said, most dialogue in a 5.1 mix comes from the center channel, but I would imagine you are trying to avoid some of that very same dialgue from the official DVDs, right?