Johannus said:
The only things that I think would work with the footage available (and I'm not saying I like any of these ideas) are either Anakin is Vader and Dooku is Anakin, Palpatine is Vader and Anakin is Anakin and we assume his actions lead to Obi Wan killing Anakin and 'Vader' (Palpatine) being responsible, or Obi Wan is Vader and he kills Anakin by removing the part where he is saved.
Who, what, when, WHY ?!
just kidding - I think the idea Qui-Gon = Skywalker works best, if one wants a prequel film before "Star Wars", Maul = Vader is possible too, maybe his relation to Obi-Wan is kind of tricky to explain (or show), but his transformation into the "half man/machine" plus battle on vulcano could work.
Skywalker doesn't even be friends with Vader, Kenobi only said, he betrayed and murdered him - thats all ...
If one trims the prequels and cuts Empire & Jedi, then there would be room for a "new" 3rd movie ;-)