"Group Video Calling" software?

I was curious to know if anyone knew (or recommended) any centralized software that can allow "group video calling" (similar to Skype), and is either cheap or free/open-source.

The group wouldn't be more than 10 people at a time (estimated 4-6 people at most per grouped video cast), and they might be people from the continental US, and Australia. Also, minimal client set up would be nice (e.g., web client plugin).

If you're a non-profit and quality at techsoup.org....look at Microsoft Lync 2010.

I'll agree with YeOldeStonecat and also recommend Lync.

However, if you're technically inclined and can stand some 'nix installation/configuration - there are two solutions that I've used with some degree of success:

BigBlueButton: http://bigbluebutton.org/

openmeetings: http://code.google.com/p/openmeetings/

Edit: I assume by "group calling" - you mean video web conferencing/

It's for group therapy for folks with social anxiety disorder. A lot of participants are not confident enough to enter a "live" group session, so this would help them get a feel for how the CBT goes. This will also help folks that are too far away, sick, or stuck babysitting.

Btw, yes, I meant video web conferencing, lol. Thank you.

I'm going to try out BigBlueButton. Maybe I'll have some success with it. Thank you for all suggestions.

You want to have only Video calling and conferencing? Polycom is the best. Not cheap but quality of video is very good. If you are looking to have web-video conferencing as well, then what I suggest is to deploy on premise web-video conferencing appliance such as RHUB appliances.