I didn't work on those 2 books but I have followed them closely and I *think* I know the difference.
The book you have covers several Ajax libraries and frameworks for ASP.NET. It also covers an early CTP release of "Atlas" which later became "ASP.NET Ajax." The newer book is exclusively about Microsoft's "ASP.NET Ajax" and is based on the final release of that. I've asked Wally to comment as well, and to take a look at the code issue.
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Wiley Technology Publishing
Jim's Book of the week: No book this week - Donate to the Red Cross!