Ikea: Purveyors of neat, inexpensive things.
Ikea NAS: Way-Cool, Low-Power, High-Capacity, Network Storage or general use computer.
Update: A little more can be found at my website post: http://aaroneiche.com/2009/03/31/my-diy-nas/ - hardware is the same, but this contains a bit more about it's use.
Update 2: The NAS has been in regular use for a few of months and has not had any heat issues. It does get occasionally warm on top. In hindsight, I think I would have preferred to put a small vent in the front to improve airflow, but apparently It's not necessary. The air that comes in through the port panel may be enough. Also, I've seen a number of people other places state that this costs too much compared to commercially available options. Please note that my price (about $310) includes a 1.5TB harddrive, because a NAS is worthless without a drive in it. So at under $200, I think it's a pretty good value, especially considering it's flexibility.
A long time back I stumbled across a website where a guy had put together a cheap DIY computer for $200. His costs went up and down a bit, but in the end he had a computer that he could not only experiment with, but also use as a back-up storage device. This was the first time I ever heard of a NAS.
Network Attached Storage is like an external hard drive. Instead of plugging it into your USB or Firewire port, you connect it to your local network. This is useful because it's accessible from each computer on the network. Given the right OS and permissions, you can control who can access it when, and even for what purpose.
Additionally, This little unit is a way to be a little nicer to the environment. All the electronics are RoHS compliant and the unit is Low Power, saving you some cash and the Earth some life.
This instructable will show you how to Build the NAS I built, and point you in the right direction for getting it up and running.