I have done this one myself over the past couple weeks (lots and lots of fun!), Johnny Chung Lee is really a genius and his Wiimote Projects are well worth a look.
You can download the software for this at Johnny Chung Lee's Wiimote Project page just like every other one of his Wiimote Projects.
This is the Wiinstrument, it's still in beta but it's coming along nicely and you can download the first versions here.
Neat little project to use with NASA World Wind.
While this isn't practical, it's still neat.