Looking for good DHTML and Ajax tutorial

I'm trying to find a tutorial that will show me how to hover a div container positioned absolutely in the middle of a page that requests interactive server side content via ajax.  I can do this in my sleep using PHP and Javascript, but I want to learn how to use the UpdatePanel AJAX Extension to do this (or whatever else might work).  Basically I want to learn the Microsoft way of doing dhtml and ajax.  Does anyone know of a good tutorial that covers DHTML and Ajax to help me get my hovering div container with dynamic content?
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