My copy of Caesar's Commentaries of the Conquest of Gaul is the Penguin Classics version translated by S.A. Handford and revised by Jane F. Gardner. So far the introduction has provided an overall summary of Julius Caesar and his motives for the conquest of Gaul. About the only thing that she lacks in her introduction is an explanation of why Caesar took upon this expedition. It was obviously for his political gains, but from who? Caesar was not a part of the Roman elite, and it is obvious from his later actions that he was not accepted from them either. So what were his motives?

(NB) I also have the Loeb edition translated by H.J. Edwards to fall back on. I am hoping that this will prove useful.