Streampad is a full-featured music application that runs inside a web browser. It gives users access to their digital music library from any computer. All you have to do is go to the website and register to create an free account, then users have to download a Java desktop application that stores the metadata from all MP3 and AC3 files it finds on your computer, so when that same user logs into Streampad from another computer, they can listen to music streamed directly from their home computer.
Also this service iTunes files on your PCs aswell. The newly released beta version allows users to stream concerts from the internet archive, create your own playlists and share them on their own site and friends and also see what their friends are listening to.. hmm Also they continue to add more features to this tool (http://www.streampad.com/newfeatures)