My understanding is that actually "pedophile" means someone who wants to have sex with young children, and "pederast" means someone who actually does have (or has had) sex with young children; note that both have the root "pedo-". So all pederasts are pedophiles, but not all pedophiles are pederasts (only the ones who actually go through with it). This terminology gets confused in media coverage, because most people just don't know the word "pederast."

At least judging from what we currently know, it doesn't look like Foley is a pedophile, but there are a whole host of other issues that make what he (allegedly) did stupid, unethical and illegal.