I'm pretty sure that widget stopped working with iTunes 6 or 7. I used to have one called ITCM (iTunes Connection Manager) but it doesn't seem to work anymore.
You can find the IP addresses of the people that are connected to your library and see what they're listening to using the activity monitor. Open it up, select iTunes, and click inspect. Click the Open Files and Ports tab and scroll to the bottom. You'll see an entry for every IP address that is listening to a song and the folder path of the song. It's not quite as convenient as a widget but pretty cool nonetheless.