Yanche if I could build something like that I wouldn't be mucking around with this forum.
There's probably something available. I'll keep it in the back of mind but I'm not going to look now or I'll end up on a two week odyssey looking at different stuff.
You could do that with what I have set up now but you would need to set the presentation up first. For example you'd set up a simple HTML slide show with links at the bottom.... image 1, image 2, image 3,etc. They could connect through the vent server we use for Coalcast and you'd be able to communicate over that. Only trouble with ventrilo server is that it only supports 10 people and by the documentation unless you want license for 1000+ they don't even want to talk to you... You could do a live broadcast but through the icecast server but that is only one way...