Even easier, you can get cheap nas (network attached storage) devices.
These are basically big disks with a small server operating system on them, and are usually very easy to set up.
http://www.buffalotech.com/products/net ... nkstation/" onclick="window.open(this.href);return false;
http://www.linksys.com/servlet/Satellit ... torWrapper" onclick="window.open(this.href);return false;
You can get 'em in all shapes and sizes.
If you're a tinkerer, go the linux route, but this will be easy and painless.