From “Marketplace” American Public Media comes an understandable explanation of how an why we are in a credit crunch.

A complicated debt package uncorked
http://marketplace.publicradio.org/display/web/2008/10/03/cdo/

"Economists are saying collateralized debt obligations are partially to blame for the mortgage crisis. What those are is hard to explain, but Rico Gagliano gives it a try with help from Senior Editor Paddy Hirsch"