If you have a Jabber ID Buddy list such as a Googletalk ID as your Buddy list and your Buddies are on PCs you cannot Video or Audio chat to them.
However check these settings first.
In the Video menu (the one to the right of Buddies and may be listed as Audio) is Camera Enabled ticked ?
Selecting it toggles the tick (and the Camera) On and Off
In the View Menu it is the same for the Show Video Status.
This makes the little green icon next your Buddy pic and some of your Buddies appear
Same for the Audio option.
Buddies without the green icons cannot Video chat.
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously