Server hardware is designed for top performance at the time (which doesn't mean much when it is several years old), reliability and massive expansion -- but other than that, it's still just a PC. It will work fine for any of the uses you mention (as would any PC with appropriate software installed on it). Although, once you see it, you may decide rather quickly that isn't anything you want running in your home 24/7. It is going to be huge, heavy, loud, and heating up the room.
Windows 2003 Server OS is the same Windows you are used to, except for additional components. Play around with it, decide what you want to have it do, post any specific questions you might have. You can find almost everything you'd want to know about it at
http://support.microsoft.com/. If possible, try to get a CD and licence key for it along with the hardware.
