I was told in this forum that the AMD chips can run as hot as that quite happily. But (IMHO) I would rather have my chips a bit cooler. It does seem a bit high for a Duron. It shouldn't matter a great deal how big the tower is, but how good the supply of cool air is. If the case has space for a couple of fans (one exhaust at the back high up and one bringing air in at the front low down) should drop the temp a bit take the stress of the chips a little and only cost a tenner.