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The page is also using LiveConnect to call JavaScript methods in the page, and seems to be including Prototype and JSON files too, so it's a good demonstration of applets interacting with other elements on the web page, something we covered in our JavaOne session earlier this month.
http://streaming.linux-magazin.de/events/apacheconfree/archive/rfielding/frames-java.htm
(Found via http://www.adam-bien.com/roller/abien/entry/it_s_not_flash_it1)