Setting up a home server running an open-source operating system is a popular and useful activity. Useful in what ways, you may ask. You could use it to run a website, collect and send e-mail messages, store your OpenID credentials or serve your music around the home.
As you can guess, we have a great many tutorials on Webmonkey for getting the most out of that machine in your closet. But here are some guidelines for the hardware side of it.