Use AJAX to validate a field

[eluser]xcristi[/eluser]
Let's say I have something as

Code:

<input type="text" name="zuzu" id="zuzu" onBlur="..."/>

A controller (without a model for the simplicity sake):

Code:

<?php

class Ajaxtest extends Controller {

function Ajaxtest() {
    parent::Controller();
}

function index() {
    return "ajax test";
}    

}
?>

and in my view <div id="test"></div>.

How can I display "ajax test" in the div above using ajax? What get to onBlur event?

Maybe there are silly questions, but have mercy, I really try to understand it.
Thanks