Suggestions for a low power and low cost file server

I want to build a system that can be used as my file server. I want something completely dedicated and will not ever be logging in locally. These are the requirements:

* As low power as possible
* Want to run either Raid 1,5, 10. (Preferrably 5 or 10) (Sata2 preferred)
* Going to use 802.11N to network it.
* Does not have to be nano itx, mini itx, or even small, but it could.
* Must be fast enough to run pgp desktop full disk encryption without major
slowdowns.
* Must be stable.

If anyone has any viable suggestions as to system components etc, then please dont hesitate.

Thanks!

Looks pretty good, but does not have any encryption. Also it does not support 802.11n. I think a gigabit interface would also be acceptable, as many of the 802.11n routers should have a 1000mbps port.