One of the questions that I keep getting is, "What is the difference between our two AJAX books?"  Let me explain the two and I think this will resolve the questions:

Our "Beginning AJAX with ASP.NET" book is about how to use AJAX technologies with ASP.NET.  In this book, we cover the basics of AJAX and how they can work with ASP.NET.  This book covers the gamut of AJAX technologies.  Along with covering the basics, we cover Sarissa, AJAX.NET Pro Library, along with a sneak peek of Atlas, which would become ASP.NET AJAX.  This book is more than just ASP.NET AJAX/Atlas.

Our "Beginning ASP.NET 2.0 AJAX" book is a fairly detailed look into the ASP.NET AJAX product from Microsoft.