What I'll be using it for:
Storing Fraps videos
IRC chat through SSH connection from school to home.
Anything fancy one can imagine to do with it
(8400GS, but a server doesn't need that.)
It'd be nice to have it so the box itself has no GUI if I were to hook a monitor up to it, but I'd like to be able to start a GNOME/KDE/XFCE/whatever session through SSH so I could use the server from my desktop PC.