Video conferencing and screensharing options for Windows [closed]

Office Communications Server 2007 This will keep the traffic inside the firewall and give you pretty good A/V conferences. Rough pricing (depending on your discount) should be in the $500 for the server and $25 per user- retail pricing can be found on the website. I know your question posed the requirement of peer to peer rather than server based but as an admin I'd much rather maintain a single server instance rather than n-number of installations (especially if it ends up being installed company wide)

Yes, Windows communication server also provides Communicator - a msn-like window for chatting within your LAN. Also has things like whiteboard sharing, etc.