Even though I have not read the book, my guess is that this is a great starting point for RIA (Rich Internet Applications -- I had to look that up)
RIA is clearly another buzzword to describe user interfaces that mimic a thick-client application. AJAX is at the core of this type of work.
As I said, I have not read the book so it may not be basic enough for someone with no AJAX exposure. However, if you understand the core concepts of AJAX and can write some AJAX code, my guess is that this is a wonderful book for you to work with. And if you haven't programmed or worked with AJAX yet, I suggest buying a basic AJAX book and then this one for your next iteration of learning.