don't buy P4 Celerons. They're <b>terrible</b> chips. for a budget PC, you're really better off getting an AMD based system.
Temperature-wise, though, as they are basically modified P4s, they'll run at about the same temps as a P4 at the same speed I guess. (so something like 35-40 Idle and up to 55+ under load, depending on what heatsink you use)
$hit Happens. I just wish it would happen to someone else for a change.