Micing the room is cheaper but introduces ambient noise. It helps to be able to move these things around. You'll probably want to buy extra speakers unless you think the ones in the monitor will do. If you get a rollabout system, you need data connections in each room you wish to use. With Vtel system, audio is sent over 1st 'b' channel.
Video goes out over the rest.
Intel said they use 16K of 1st 'B' for audio. Data has priority over video on the rest of the pipe. Additional Reading Vistium Desktop Videoconferencing Training - Good training resource for teachers using videoconferencing. Videoconferencing for Learning - A page a lot like this one, but much more detailed. The main topics raise issues you'll need to address in putting together a videoconferencing system.