Skype.
Audacity.
This.
I did something on Skype a few weeks back and was really impressed with the way four different people were able to sound like they were in the same room despite being in different states.
I use Audacity to record everything, and you can use a few plug-ins to make the thing really sound good and professional. If you learn how to use Audacity and all of the tricks therein (I use the noise reducer and compressor/limiter functions quite liberally), you can produce a pretty good broadcast.