help! iChat AV problems

[Paul Bernhardt]

I've got iChat AV problems.

My Dad's computer can do text iChat/AIM just fine. But, whenever he and 
I try to do a video chat there is a lack of handshaking of some kind. 
His computer will put up the accept the chat dialog, but when he 
accepts it he gets a message that says I am not responding. Similar 
behavior if he tries to initiate the video chat.

Any clue what could be going on? How to fix?

Systems: His end: eMac, iSight camera, OS 10.3.3 with latest updates.
My end: iBook G4, iSight camera, OS 10.3.3 with latest updates.

Paul