You may be unable to participate in a video or audio chat in Mac OS X 10.5 Leopard on PowerPC-based Macs that have an 867Mhz G4 processor. The iChat Video menu may not appear, and under the Connection Doctor's Capabilities tab your computer may be listed as "unable to participate in a video conference" due to bandwidth/network issues.
You may also receive an alert when you attempt to respond to a video conference such as:
"NAME has invited you to participate in a Video Chat, but your computer does not support video conferencing."
(Where NAME is the name of the buddy that invited you to the video chat.)
Download and install Mac OS X 10.5.2 or later.