PHP AJAX HOW-TOs

When I visit programming talk I find out a hot topic talking about Levyo Ajax Technology Gallery. Their site is at http://levyo.com - demo at http://gettingzone.com. They build Ajax application on PHP, Mysql. Their gallery runs so fast, especially when I login, register, submit, rate, write comment, upload, process, Tab feature... It's great.
How can they do especially "unlimited tab feature", you can add new category in Admin CP, it generates new Tab automatically? How can we programm an Ajax Application on PHP?

To put together a web site/application that makes use of Ajax techniques, you will need to have a good understanding of JavaScript, PHP or some other server-side technology and an understanding of the mechanism you are going to use for passing the information back and forth.

If you go to the XML... forum, you will see a number of threads already started on Ajax, the response to which include various links to useful site and infromation.