Y!, thanks for the clarification on that. (About an hour after I installed Paresan I got told of a way to do other IMs, that works on RO Firefox. www.meebo.com very slow though).
Audio. It can't be only a patented codec because I have talked to people on MSN with my SIP using G.711 using GTalk2VOIP.com as far as I can tell they just negotiate the connections. I didn't think they actually proxy and convert. But what I was wondering would be if it were a realistic proposition to do something similar with a client (it either establishes a connection and hands over or forwards the data.)
Video. Just incoming would be a nice start. I would think that just sending a sprite or a slide show of sprites would be useful in the absence of a webcam. There were video capture podules, I have one if it would be any use to you.
File transfer. Will the interface be drop the file in the message field to send and drag the icon from the message window to save incoming, perhaps with a preview of pictures?