We have setup a small home file server using Ubuntu. I used an old defunct desktop computer and installed Ubuntu 7.04 alternate. The server is quick to start and easy to shutdown with just one push of the power button. Most of the setup has been done using a very easy web-based interface.
It is a great server for sharing files in a home setting, and it would also be a great system for a small business. For the sake of brevity, I am not going to go into the whole setup process here. Feel free to drop me an email if you would like more information.