Your bandwidth would be the real limit here, I can't see the hardware being pushed beyond what your internet connection can cope with (unless you've got a 5Mbps+ upload connection).
To get most use out of that server you could turn it in to a media centre using some software like XBMC :
http://xbmc.org/. That way you can store all your music, photos and videos on it and access it in your home on a TV (assuming you can connect your server to a TV with the right graphics card and cables).
If you want to run a web server, you'll need to download some webserver software (probably apache or IIS). However, there is a very easy bundle called XAMPP which contains everything you need to run a webserver in a single package. I'd only use it for a test environment though, but it's great to understand how things work.
You can download XAMPP here and read up on all the docs to see how it works
http://www.apachefriends.org/en/xampp.html