This interweb thing is great! I've been translating a bunch of strings in our software at work from English into French. We used a translation company for most of it, but these are the little bits that got left out. Not sure my translations will be perfect, but they'll get what they get. Anyway, I've been relying heavily on a few fantastic web sites.
WordReference.com is your standard dictionarytool, but it's quite comprehensive and fast.
The government of Quebec provides the fantastic Grand dictionnaire terminologique which has an exhaustive range of technical term translations in just about every technical field you could imagine from aeronautics to zoology. You have to be careful though, because Quebec French isn't always the same as French French. For example, the standard translation of email in French French is "courriel" while in Quebec they say "courrier electronique".
Finally, and probably more useful for someone who's a bit rusty in French these days, is Verbix which conjugates verbs into the 15 main tenses. Incredibly handy, particularly when you don't have your red book to hand.