CC.Net I have used a few projects back and thought that it was great. I really like the instant feedback it provides and it makes total sense that you would want this as a gadget. System tray was the old way (on desktop non obtrusive) but gadgets provide the push interface with the ability to provide functionality at the same time.
I went hunting for the equivalent TFS gadget. I discovered how to build
I was pleased to see Paul Stovell’s locally built Team Build Vista Gadget
The only other tool I found on my quick search was the TFS Query Tracker