Somebody discovered that the themes used in Google Talk can have javascripts enabled. They already rolled out a theme that would google the selected word if u click Enter on ur chat. And also a theme that would automatically convert emoticon text to pictures.

oops .. forgot to post the links:
http://www.customizetalk.com/forums/viewtopic.php?t=487
http://www.customizetalk.com/forums/viewtopic.php?t=495