This looks interesting. Dimdim web conferencing is removing usage restrictions from their open source version. I also think it is a smart move on the part of software vendors (open source or commercial) to make VMWare appliances available. I am already downloading the Dimdim appliance and plan on testing it myself.

In the next week we will release a new version of the Dimdim Open Source Community Edition to SourceForge.net.  (UPDATE: our new Open Source release is now available) That version is on par with the features of our hosted offerings, removes the 5 attendee limit, enables multiple simultaneous meetings and even adds a 2-way video chat feature. We have also packaged the Dimdim Servers into a single VMWare Virtual Appliance to ease the installation process.  You'll also notice much improved documentation and a new admin console.

Dimdim Blogblog