A good starter tutorial in that direction lies here. And another one, a Flickr Gallery.

However, if you belong to the population of web developers who are not psychic or lucky, you would probably have something like this staring your face when you try the above tutorials -

Fatal error: Call to a member function on a non-object in [...]/cake/app/views/layouts/default.thtml on line 8

That’s because both the tutorials do not explicitly mention that you need to declare the AJAX helper in the controller file if you are going to use AJAX features. The best way to do that is to copy the app_controller.php file from your cake/ directory, put it in your app/ directory and add the following piece of code to it:

var $helpers = array('Html', 'Ajax', 'Javascript');