Check our extensive discussion on educational IRC conferencing . This technology is fairly new, so tolerance and patience are important. If you want to share live images and sound, you need a digital camera, an AV computer, and conferencing software such as CU-SeeMe. You can hook a camcorder directly into an AV computer, increasing the quality and range of your broadcast. But the audio can be pretty choppy.
Some folks like to use a telephone conference for when the audio is going to be extensive.
Information and software are available from White Pine and freeware from Cornell University. Another great place to find this information is at Global SchoolNet's CUSeeMe pages.