Yup, it went a little bit like this:
VOICE OF VADER - James Earl Jones (duh)
BODY OF VADER - Dave Prowse (EP IV, V, VI)
FIGHTING VADER - Peter Diamond (most likely... in EP IV) .... but Bob Anderson in EP V and EP VI
There is some debate whether there were a few stunt doubles / extras / stand-ins for Vader in many cases (and there was even a stunt double for Luke during FIGHT ACTIONS---and not just the flying out window--in Episode V), but it's sometimes hard to say.
Why is it hard to say? Well... apparently, LFL didn't really properly CREDIT some of these guys. In fact... I don't even think Bob Anderson *WAS* credited (officially, in film credits) originally. But IDK. It gets complicated.
As for saber fights in films... this is the same conversation as always... IT'S STAGED/FILMED COMBAT. Always governed by the choreographer at hand, the performers themselves ("style") and their experience/training/strengths/weaknesses... and what the director asks for/wants.
In EP IV, we saw an entirely different and interesting "style" of the choreo. I just finished doing the Obi-Wan v Vader fight for several live performances, and... it was a lot of work... but fun, too. :) Video coming soon.
EP V's style changed due to the choreographer changing, AND because Mark Hamill & Bob Anderson were able to convince George Lucas that a few one-handed actions could add variety and fun to the fight... which GL was originally vehemently against.
This style carried through EP V... but if you'll notice... in EP VI... there are (once again) almost *NO* one-handed actions! :) Did anyone ever note that? heheheh I found it interesting.
Anyhow... yeah... bottom lines are:
* You have to be dedicated
* You have to put in the work
* You have to look at others' work and "what has come before"
* You have to train (and experiment) on all the aspects of saber combat (which I've categorized as a GUIDE, many times before)
Pretty much training & dedication with saber spins & poses... attacks & defenses... general MA moves (kicks, punches, elbows, jumps)... paired choreo... and paired sparring. Finally, somewhere in there... if you're "alone"... you have personal forms, which can actually contain actions present in all of the ones I just listed.
Granted... personal forms cannot prepare someone (much?) for something like sparring or staged/paired combat. Mainly because you have to learn to work WITH others during such paired work, and... everyone is different!
http://www.youtube.com/watch?v=tOuCbDkKIs4HAN'S MY MAN! :D