You might not be able to do this since you have a Duron, but I made my server a lot quieter by replacing the heatsink+fan combination with just a heatsink. Mind you, my server runs a Pentium 100. :-) And it took me many months before I found a Pentium with only a heatsink.
Perhaps you could rummage in Google for [link|http://www.google.com/search?hl=en&lr=&ie=utf-8&oe=utf-8&q=fanless+CPU+heatsink&spell=1|heatsinks without fans]. Like [link|http://www.pcstats.com/articleview.cfm?articleid=627&page=3|this], perhaps?
Wade.
P.S.: I just found [link|http://boozhoundlabs.com/bigsink/|this]!