I have said several time before here but I'll say again
If you are looking for a really small & quiet headless server then take 
a look at the much maligned Mac Mini
I have three of these now. Two PPC versions and one Intel. I got them 
all of Ebay. The last PPC one was 110GBP.
I have added a Lacie Firewire HDD to two of them. Again almost silent.
They sit on the shelf in my Office serving
 - Aldershot & Farnham CC Picture Gallery ( 
www.afccweb.net is hosted by 
One & One but the pictures are served from the Mac Mini in my Office.
 - My local Email Server (axigen) in a VM
 - My local WIKI server + Bugzilla + SVN In a VM
 - My Bacula Server ( Two 500Gb Firewire HDD's hold the backups )
 - My Music Server
etc.
One of the PPC devices is a backup for the other one that serves the 
Picture Gallery.
The OS on all of them is Fedora 9 (PPC) or CentOS(Intel)
The PPC ones run Linux pretty well completely OOTB.
Stephen D