Cross Platform Way to Broadcast Speakers’ Laptop Sessions

I am looking for solid ways to screencast my user group’s speakers’ laptop presentations (e.g. some sort of an open source version to GoToMeeting or maybe a video equivalent to Shoutcast / Icecast).

Since I’ll be using my company’s conference room, I’ll have a decent speaker phone. But since my company’s network and bandwidth is not really conducive to hosting stuff internally, I’m hoping to be able to stream out to some collocated server, and then everyone can connect to that server directly to see the presentation.

(Icecast + Theora look like a promising combo, but I have yet to implement either)