For those who haven't seen it, there is a slick NAS server software based on m0n0wall here - http://www.freenas.org

What I would like to do is build a small appliance based on this software that could house a pair of 500Gb drives. I'd rather not use a PC unless it's the only way to do it. Something the size of a Snapserver would be great!

Here is what I would like:

Gigabit Ethernet
Run FreeNAS from a CF card
Low power (barely above hard drive requirements)
Video & keyboard not necessary, assuming a serial port is all I need to configure.

Is there a box like this on the market, or something that can be built?

-Robert

you'll probably want to look at the family of mini-itx formfactor mobo's. They largely are split into two parts - media and industrial. check mini-itx.com to see what's around for your needs. a small cube case or something should sort you out fine for a case (although my one runs in a Snes box) and the power consumption is seriously low, and some boards completely run fanless.