Garrett's article mentions several technologies that he sees as parts of an Ajax solution. These are:
HTML/XHTML: Primary content representation languages
CSS: Provides stylistic formatting to XHTML
DOM: Dynamic updating of a loaded page
XML: Data exchange format
XSLT: Transforms XML into XHTML (styled by CSS)
XMLHttp: Primary communication broker
There is one major component that Garrett neglected to mention in his article: the necessity of server-side processing. All of the previously listed technologies relate directly to the client-side Ajax engine, but there is no Ajax without a stable, responsive server waiting to send content to the engine. For this purpose you can use the application server of your choice. Whether you choose to write your server-side components as PHP pages, Java servlets, or .NET components, you need only ensure the correct data format is being sent back to the Ajax engine.
The examples in this book make use of as many server-side technologies as possible to give you enough information to set up Ajax communication systems on a variety of servers.