Hi,
It will be worth opening the Activity Monitor (Applications/Utilities) and seeing if iChat itself or iChatAgent is the app that is ramping up the CPU usage. (Also keep an eye on vcencoder during Video chats).
Any issue with vcencoder will be a Video production issue.
I would check any Add-On Effects and Backdrops you may have.
These are stores in Hard Drive/System/Library/Compositions
(MoreiChatEffects should not really put them in here but it does. Add-ons should go in the corresponding folder in Hard Drive/Library/Compositions for all Users or Home Folder/Library/Compositions for Single User use)
iChatAgent deals with Login things and handling background stuff for iChat such as launching vcencoder and linking in the Framework parts as they are needed. (it is therefore a bit more difficult to say where the issue is that it is having.
This maybe reported in Console though (Applications/Utilities)
iChat sort of "swans about" telling everything else what to do and when to do it.
It is responsible for displaying the various windows.
Console again may indicate Messages about iChat that can help.
7:22 PM Saturday; August 6, 2011
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb( 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously