Astronomy Cast.
http://www.astronomycast.com/page/7/
This is a really good series of Podcasts. Scroll down to the bottom of the page a listen to the one on Pluto.
You don't need an mp3 player to listen. Windows Media Player is all you need.
Just click on
'Download Episode 1 - Pluto's Planetary Identity Crisis (12.6MB)'
enjoy.