Issues with iChat, Jabber, and Comcast WCG200-CC wireless router

I'm trying to help a remote colleague connect to our iChat server (using Jabber, not AIM) from her home. She has a Comcast/Linksys WCG200-CC wireless router. We've tried port forwarding and putting the MacBook on the router's DMZ. We've also tried lowering iChat's bandwidth to 200 kbps. She is able to send text messages, but attempts to connect via audio or video fail.

If I try to call her, she never receives the invitation. If she calls me, I receive the call but she doesn't receive notification that I've accepted the call. Knowing what bit I know about iChat's use of ports, my guess is something is not getting through to her on port 5060 and/or port 5678.

Another colleague lives in the same state and is also on Comcast, but does not have this particular model of router. She is able to connect with others without problems.

I know this is an atypical setup, but we need to get this to work for an educational research project we're working on at the University of Kansas. Does anyone have any ideas?

Thank you in advance for any advice.