Just get the "Call of Duty and Call of Duty: United Offensive" pack. Call of Duty and then its expansion. There are definitely servers for United Offensive, Call of Duty on the other hand, I know there are, but the question is how many there are.
There are several patches out for both games, so if you get on and see NOTHING patch it. I use codfiles.com for patches, skins, maps, etc.
to a fellow CoD player (well, soon at least). I play CoD2, I like it the best out of all those.