A few weeks ago I was contacted by one of our colleagues at UNC asking for a meeting about DigitalForsyth. We wanted to be able to show them how the web-interface worked but nobody wanted to do the travelling so we decided to try DimDim (http://dimdim.com) a quasi-free web-meeting application.
DimDim supports one host and up to 20 participants in the free version. It supports website and desktop sharing, voice and video over tcp/ip, and a few other moderator tools.
There are some other tools that you can use for person-to-person video sharing (such as google talk or skype) but dimDim did a great job sharing our desktop out & helping with other presentation features.