We've recently had some problems with the chat at http://webconf.egrn.eu. Because of this I've created a chat room in Jabber called cdfg@conference.jabber.org. Jabber can be accessed using any number of clients (http://en.wikipedia.org/wiki/List_of_Jabber_client_software) including web-based ones such as http://www.gotoservers.com/chat/ It should thus not be problematic to use on office machines where no software installation is possible.
The procedure is to login with any suitable login / password combination on the server jabber.org. Once done that choose group chat and enter the room name cdfg@conference.jabber.org where you'll meet the others. Some, though not all clients even support a whiteboard and voice chat.
My login is mwkuster@jabber.org