Raed "The Valacchi Papers" by Joe Valacchi and Peter Maas.

Valacchi was the first mobster to go public (late 60's) by exposing the inner workings of organized crime to a senate committee. It was in his testimony that Americans first heard the term "Cosa Nostra". The book goes into his whole life in the mafia -- he was a soldier in the 20's and 30's, and there's some great stuff on the Castalalmerese (sp) war, the original organization of the 5 families of NY, how they were set up with capos, soldiers, etc.

It's probably out of print, tho, and might be hard to find, but its well worth looking for. It was also a movie with, I think, Charles Bronson.