Its an easy tutorial to create a simple sign-up form, when the user put his mail address on the text field and using Ajax we will update the user with thanks message and will store the address on an existing mysql database

This script loads content from the server and inserts it into an empty HTML element(example a DIV tag) on your page. New pages can be appended dynamically and the script will scroll down to the content of the new pages

Although I get the feeling that a few people are perhaps a little over-excited about it, the recent release of numerous high-profile Web applications that use remote scripting has shown that there are definite advantages to utilising these techniques in the creation of seamless Web applications, and to augment Web page functionality.

This article aims to give you an introduction to the foundations of remote scripting, in particular, the emerging XMLHttpRequest protocol. We'll then walk through an example application that demonstrates how to implement that protocol, while creating a usable interface.

Ajax is changing web applications, giving them a responsiveness that's unheard of beyond the desktop. But behind all the hype, there's not much to Ajax -- (X)HTML, JavaScript, and XML are nothing new, and in this tutorial, I'll show you how to simplify the process of adding Ajax to your application even further with the help of jQuery, a popular JavaScript library.

Many webmasters want to make polls in their websites, making it with a normal script (php, or .net) is a very old fashion, now you can make it using Ajax technology for no page refresh and very fancy effects.
just include the script in your code and look at the results.
this article rounds up the top ajax poller scripts. Enjoy