Microsoft Learning has a free two hour AJAX Clinic.
Title: Clinic 5230: Developing Enhanced Web Experiences with Microsoft® ASP.NET AJAX Extensions
In this 2-hour clinic you will learn about the rich functionality that ASP.NET AJAX Extensions provides for building highly responsive and enhanced web applications. In addition to learning about the different server and client components of ASP.NET AJAX, you will also learn how to build new ASP.NET AJAX applications and how to upgrade existing ASP.NET applications to take advantage of ASP.NET AJAX.
This clinic is appropriate for experienced .NET Web Developers and Software Architects who are looking to incorporate ASP.NET AJAX within their existing and future solutions.
[found via Chris Breisch]