Playing your music over the internet
TwonkyVision
My NAS uses TwonkyVision as a UPnP server.
TwonkyVision also offers a web interface (http://IP_Nas:9000/webbrowse)
If you use port forwarding on your router, you can browse and play your music over the internet using this interface.
Windows 7
A new feature is too access your media at home over the internet.
You need a Windows Live ID to do so.
A setup guide can be found here: http://www.neowin.net/news/main/09/03/12/windows-media-player-internet-access-to-home-media