This add-on requires growl (http://growl.info/).

When Songbird plays in the background you should see track notifications appear. To change how the popups look check the Growl pane in your System Preferences.

matt (http://blog.songbirdnest.com/2006/11/13/growl-support-just-like-everyone-else/) made the 0.1 version of this add-on. i just made it work in songbird 1.2.