Apparently this one will run from Chrome so, if you're like me and have 3, 4 or 5 GTabs open at any given time, each tab doesn't pop up with a Chat window.
Never tried the Apps gadget, to be honest. I have an apps account, but since this is the account tied to my Android, this is the one I use most of the time.
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http://howto.cnet.com/8301-11310_39-57384232-285/how-to-use-google-chat-from-your-desktop/