I love it when a great new application comes along and is open source. The guys from DimDim, have created a Webex and Livemeeting like application that is open source.
www.dimdim.com
I was using, www.vyew.com but will give this a try. In my initial trials it has worked well. You can share your desktop with a remote person. Upload documents (PPT and PDF) and share with someone.
This is a very powerful and useful tool.