FOSS Multi-Party Videoconferencing Solutions?

[Charles Jones]

I'm currently looking for a solution that will allow multi-party video 
conferencing.  Here are some preferred features:
* Ability to hold a video conference with more than 4 attendees
* Ability for multiple, seperate meetings with more than 4 attendees 
(probably max of ~15 people using system at once)
* Usual features like desktop/application sharing, whiteboard, text 
chat, VOIP
* Clients for Win, Mac, and Linux (most of the clients are Win32 but 
definitely a few mac and linux users)
* Easy to use for non-technical people (not VideoLAN)

I've found some solutions that work great, but would rather not use 
because of either a large monthly expense, or is Win32-only. If the 
solution requires a dedicated server on a big pipe, that is fine.

If you know of any FOSS solutions, or even one that costs money, please 
let me know.
-Charles