the ol' desktop just blew up

So I need to get a new one and need some suggestions on what to look for. Basically I don't need anything top of the line I just need something thats decent that I can download music and movies to. It would basically be my "back-up / downloading computer" so I don't want to spend a fortune on something that's going to be getting viruses.

So any suggestions on what the computer should have in it as far as memory etc etc.