Instructions: Start iChat, then start the "Switch Icon" script and reply to the dialog asking if you have GraphicConverter installed (for nice cropping). Then enter an initial search string (i.e. red porsche or Mac G5, etc.) and it will start cycling a new icon every 10 seconds.
The second script, "Switch Icon Query", is a two-liner that can be placed into the script menu and will just reset the query string to something different.