First step: recording audio. See Audacity.
Second step: recording both sides of a conversation. There's a bunch of 3rd party applications. See http://webcastacademy.net/presentations/upei2007
- Recording Conversations with remote participants
None of these programs capture both ends and push it out.
Use Virtual Audio Cables - Tools
Then streams out to shoutcast server using simplecast. (Or an open source program called icecast (but it doesn't support mp3 well))
or freecast.com - http://freecast.co.uk
You're essentially using nicecast - http://www.rogueamoeba.com/nicecast/
Jing - http://www.jingproject.com
Screen sharing - live sharing of computer screens
ustream.tv - free hosted service
To connect audio and video to computer - Pinnacle device - takes audio and video cables in one side, and provides a/v computer inputs out the other side.