low power linux PC?

[Peter Dobratz]

So I want to setup a linux server at home to do backups from various
computers around the house.

Amanda looks promising ( http://amanda.zmanda.com/ )

For the backup server, I want to setup a separate box, probably
running Debian.  As the primary purpose of this computer is just to
store the backups, my primary feature consideration is power
requirements.  Is there anything out there that can run Linux, have a
few 250 GB or greater hard drives, and run on around 50 Watts or less?
 It can be a headless box that I ssh into.

Thanks,
Peter