Darth Jello
Cheese Spelunker
Based on the tie-in comics that are supposed to be fairly cannon, Xavier doesn't meet Magneto until 1992 and the have their falling out shortly after the construction of Cerebro and after Xavier recruits Jean and Beast.
Here's my idea for the movie (taking much of it from the comic in question)-
The first half should deal with Max Eisenhardt in the camps and his killing several SS officers and letting the man who killed his parents (I believe his name was Hans Von Schenk in the comics) take the blame. He escapes during a revolt and reunites with his childhood love, Magda. They're married, the incident with Anya happens and he's forced to take on the Erik Lensherr identity to escape prosecution for the massacre he commits. He then goes into work for two decades as an agent of a secret agency pursuing Nazi war criminals including a mutant who experimented on inmates-a British defector named Nathan Essex whom the other inmates called Nosferatu or Sinister because of his vampire-like complexion and who used magneto's powers for experiments bonding metal to bone. He leaves the service in disgust after his commanding officer- a young William Striker, uses him to capture Essex and then negotiates immunity for him in exchange for his research on mutant prisoners and the process of bonding metal to bone.
The second half would cover everything in the comic involving Erik becoming friends with Xavier, the beginnings of the X-Men and him searching for Von Schenk, finally battling Sinister and coping with the fact that he was obsessed with capturing people who committed atrocities when he himself killed an entire village. His mutant supremacy evolves from a rationalization of his own actions. Sinister should be the one to cripple Xavier in the final battle of the film.
Casting ideas:
Ian McClellan-Erik Lensherr
Patrick Stewart-Charles Xavier
Jamie Bell- Young Erik Lensherr/Max Eisenhardt
Zooey Deschanell-Magda
Danny Huston-William Stryker
Sean Penn-Sinister
Christopher Lloyd- Von Schenk
Haley Ramm-Jean Grey