Problem with Ajax Helper in Cake PHP

I am trying to implement the Ajax feature in the comments section of my blog. I have downloaded prototype- and have placed it in the js folder inside webroot.
I have made the following changes in the layout file(default.ctp)


Also, following code has been added to controllers

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

This is my code in the posts_controller.php file

function view($id = null) {
    	if (!$id) {
    		$this->Session->setFlash(__('Invalid Post.', true));
    	$post = $this->Post->read(null,$id);
    	$comments = $this->Post->Comment->find('all',

My code in view.ctp file


<?php foreach($comments as $comment): ?>

<?php echo $comment['Comment']['name']; ?>

<?php echo $comment['Comment']['content']; ?>

<?php endforeach; ?> <?php echo $ajax->form('/comments/add','post',array('update'=>'comments'));?> <?php echo $form->input('');?> <?php echo $form->input('Comment.content');?> <?php echo $form->input('Comment.post_id',array('type'=>'hidden','value'=>$post['Post']['id']));?> <?php echo $form->end('Add Comment');?>

I have added the following function in the comments_controller.php

function add() {
    	if (!empty($this->data)) {
    		if ($this->Comment->save($this->data)) {
    			$comments = $this->Comment->find('all',array('conditions'=>array('post_id'=>$this->data['Comment']['post_id']),'recursive'=>-1);
    				} else {

And following is the code in the add_success.ctp file

<?php foreach($comments as $comment): ?>

<?php echo $comment['Comment']['name'];?>

<?php echo $comment['Comment']['content'];?>

<?php endforeach;?>

Now the problem is that I am not able to add comments. Nothing happens when I click on the add comments button. I have manually added comments in the databse and that works. But I am having problems when I am trying the Ajax Helper.

Where is the problem??And guys, sorry for such a long question.[:(]