How use AJAX in DRUPAL

<?php
/*product.module*/
 
function product_menu() {
 	$items = array();
 
	$items['product'] = array(
		'page callback' => 'drupal_get_form',
		'page arguments' => array('product'),
  		'access arguments' => TRUE,
  		'type' => MENU_CALLBACK,
 	);
 
 	$items['product/check_name'] = array(
  		'page callback' => 'check_name',
  		'access arguments' => TRUE,
  		'type' => MENU_CALLBACK,
 	);
 
 	return $items;
}
 
function product() {
	$path = drupal_get_path('module', 'product');
	drupal_add_js($path . '/product.js', 'module');
 
	$form['product_name'] = array(
		'#title' => t('Product Name'),
		'#type' => 'textfield',
		'#required' => TRUE,
		'#size' => 30,
		'#description' => t('Please enter product name.'),
	);
 
	$form['check_name'] = array(
		'#type' => 'markup',
		'#value' => "<a href='#' id='check_name'>" . t('Check Product Name') . "</a><br/>",
	); 
 
	$form['status'] = array(
		'#type' => 'markup',
		'#value' => "<span id='status'></span><br/>",
	); 
 
	$form['submit'] = array(
		'#type' => 'submit',
		'#value' => t('Submit'),
	);
 
	$form['cancel'] = array(
		'#type' => 'markup',
		'#value' => l(t('Cancel'), 'product_mgmt'),
	); 
	return $form;
}
 
function check_name() {
	$name = strtolower($_GET['name']);
 
	$query = "SELECT COUNT(*) AS total FROM {product} WHERE LOWER(product_name) LIKE ('%s')";
	$rs = db_query($query, $name);
 
	$info = db_fetch_object($rs);
	$total = $info->total;
 
	if ($total) {
		echo "$('#status').html('This product is available.');";
	}
	else {
		echo "$('#status').html('This product is not available.');";
	}
}
?>

/*product.js*/
 
// JavaScript Document
$(document).ready(function() {
	$('#check_name').attr('href', 'javascript:void(0);');
 
	$('#edit-product-name').keydown(function(event){
		$('#status').html('');
	});
 
  $('#check_name').click(function() {
		var name = $.trim($('#edit-product-name').val());
 
		if (name == '') {
			$('#status').html('Please enter product name.'); return;
		}
 
		$.ajax({
  			type: "GET",
			url: "/product/check_name",
  			data: "name=" + encodeURI(name),
  			success: function(msg){
				eval(msg);
  			}
 		});
	});
});