Here is Ajax Login Module I wrote with YUI and an Open Source Template
1. The main page (index.php)

<div id=‘loginDiv’>

        <?php

        if((isset($_SESSION[‘userName’])))

        {

                echo ‘<h4>Logged In<span> As</span></h4><div id=emailDiv>’.$_SESSION[‘userEmail’].‘</div><input type=’submit‘ value=’Logout‘ class=’button‘ onClick=’doLogout();‘/>’;

        }

        else [...]