Jeffonthego: That was beautiful. I so completely agree!
Mini-rock: thanks for your compliments on my take on how it all happens. I think Jeffonthego added to Anakin's psychology and philosophical state of mind for these occurences, but the emotional drive to "save everybody" (running after Mom and then Obi-Wan in AOTC, then Obi-Wan again and finally Padme in E3) will be the emotional straw that breaks his back. Together, these elements combined, as perfectly stated in Jeff's post above, will create Darth Vader.
Just know that I know NO spoilers. I can't confirm anything I put in my last expose above. I just think that it logically makes sense if it goes down that way, and we'll still preserve the punch in ESB for future generations who may watch these movies in Episode Order.
The only thing it denies the fans is learning who built the Darth Vader suit, and who or what (droid?) physically put Anakin into it, and what on him is mechanical (in addition to his lungs on ventilators and his bionic right arm - these could be it alone, too, you know. The point is WE don't know yet. Only George really does. And making Vader more and more mechanical is not really important to the story. So it'll likely never be shown, so read your books my friends, and keep enjoying them for years to come. (Del Rey, Dark Horse, Scholastic, and DK will certainly enjoy their profits for years to come - I'd garauntee that!)