The server side language is PHP and is the easiest Web language to learn. You set up PHP, Apache, and MySQL on any computer for the AJAX experiments. You can then use the PHP/Apache/MySQL for many other Web related experiment.
Chapter 1 covers the background and theory.
Chapter 3 covers the PHP part in the server including security.
The next chapters cover AJAX for form validation, suggestions and autocomplete, realtime charting with SVG, a grid (or table), an RSS reader, plus drag and drop.
There is an appendix covering installation of the required software on each operating system. There is mention of an online appendix where you can see examples working.
There is everything in this book to make you productive with AJAX.
There is a second edition. The second edition introduces unnecessary complications in the PHP code and, apparently, forgets security. I have not tried the second edition. The second edition PHP part introduces classes, objects, and stuff that should be in a PHP book, not an AJAX book. The extra PHP complications squeeze out some of the AJAX explanation. I find the first edition good for beginner and intermediate Web developers. User reports about the second edition suggest you need a good knowledge of PHP to understand the PHP code in the second edition.