How to build a cheap and fanless server [closed]

Any advice about how to build a cheap and fanless server? It's main uses would be web and file servering, but it could be a day when I'd like to add some streaming and mailing capabilities as well.

OS of choice: GNU/Linux

Take a look at Atom powered devices. Atom N330 should be powerful enough to do most of the home server duties, and it is relatively cheap and consume just a bit of power. Not to mention that it doesn't take much space either.

I'd look especially at Acer Revo R3610 but there are completely fanless models available.

You can see many references at Silent PC Review. They're more concerned with eliminating noise, not minimizing cost, but you can pick and choose from what's available.

I don't know your definition of cheap, but a Pogoplug may just fit the bill.