The more I find out about the background of Dooku as explained through the various books (I haven't read them but I've gotten second hand info from a friend), the clunkier it sounds. From what I hear, and please correct me if I'm wrong, Dooku was an honest to goodness Count by right of birth. But presumably his facility with the Force was identified at the typical young age and he was recruited into the Jedi. BUT he later appears to have left the Jedi without much fanfare (He RETIRED?!

) and went back to wherever he was royalty and started being the leader of the Separatists. Later the Jedi act all baffled by who this guy is and, as I've said before, he's mentioned as being "The Mysterious Count Dooku" in the opening crawl for EpII.