SheevaPlug Dev Kit from Globalscale Technologies: £60 + £20 shipping from US + £20 VAT.
Comes with Ubuntu 9.04 preinstalled.
Power on, connect to ethernet.
Look in local router's admin pages to see what IP address the Plug was given.
ssh root@IP_ADDRESS (password = nosoup4u)
Misc fixes from Plug Wiki: fixing the existing Ubuntu install.
apt-get update; apt-get dist-upgrade
aptitude install psmisc (for the killall command)
Set up Deluge as a thin client (installs a fair amount of GTK/X11 stuff, not sure how to avoid this)
Configure the deluge GUI on another machine to point to the remote deluge daemon.
Set up the InitScript for deluged.
Connect an SD card, USB drive or network drive for storage.
/mnt on the Plug is shared automatically by Samba, so if deluge is configured to save downloaded files in a folder in there, they'll be accessible from other machines on the network.
Can also create a directory in /mnt, autowatched by deluge, to put torrent files in from other machines.
For the deluge Web UI:
aptitude install deluge-webui; /etc/init.d/deluge-daemon restart.
Connect to http://IP_ADDRESS:8112 and change the default password from 'deluge'.
Install a DAAP server?
Please note: this was a first attempt; there might well be better ways of doing some of this.