I have been wanting to do something similar.  I want small, quiet, low power
and always ON and on my LAN.  I had been wondering if anyone had tried
putting FreeNAS:
    http://en.wikipedia.org/wiki/FreeNAS
on a SheevaPlug:

http://gizmodo.com/5159399/sheevaplug-a-99-linux-pc-crammed-inside-a-wall-plug
(or something similar) with an external USB or esata drive

-- 
Dazed_75 a.k.a. Larry

The spirit of resistance to government is so valuable on certain occasions,
that I wish it always to be kept alive.
  - Thomas Jefferson