This is part of one of many such tutorials covering Ajax with Prototype.
If you do not want to get your hand to dirty with custom Ajax code, then using the extremely handy toolkit from prototype may be perfect.
In this simple example I’ll show you just how easy Ajax calls are. But you will need to have your own copy of prototype (its free!).
On with the example
From : http://www.ajaxtutorial.net/index.php/2006/11/29/simple-ajax-using-prototype-part-1/