Very usefull resources:
http://www.johnwiseman.ca/blogging/?p=61
This one shows you how to use PHP and AJAX to connect to MySQL
http://www-128.ibm.com/developerwork...jaxintro1.html
Mastering AJAX
Part 1 from IBM
http://www-128.ibm.com/developerwork...07AJAX-Request
Mastering AJAX
Part 2 from IBM
If you find any more free tutorials post them here! I'm eager to learn more about AJAX.