I tried Babel Fish anyway, and it did a decent job, although some of the phrasing was very peculiar.
I typed my response to him in English and included an explanation of how I was translating, then I ran the response through Babel Fish and sent it on it's way.
It wasn't a hugely important E-mail, and if Babel Fish translated my words to French the way it translated his words to English, then I'm sure he got a good chuckle out of my reply.
Thanks again everyone for your help.