detecting which dataRef the mouse is over

In a simple 2D plotter built with visad, I'd like to detect which 
line (or lines) the mouse is over.  I have registered a DisplayListener
on the Display, but I am uncertain how to do two things:

   - detect mouse motion events (now I just get MOUSE_PRESSED and RELEASEd)
   - figure out which line the mouse is over
   - display a small tooltip-like tranisent window on top of the display, 
     announcing the name of the line.

Tips on any of these points will be most welcome!

 - Paul