Sometimes a bit of software just blows your mind iCommune is one. A seemingly mild-mannered plug-in for Apple’s iTunes music software, it turns iTunes into a streaming peer (that also, incidentally, allows you to copy MP3 files).
The weak spot is that the user must manually enter fellow peers to stream from/to: there’s no auto-discovery. But once they’re in there, your friends’ music is just as available to you as the music on your hard drive, through the same interface. The simplicity is very powerful. This may be part of the reason Apple forced the author to pull the plug-in. But if you can find a copy, check it out.
And let me know what your IP number is so we can share.