Create an Ajaxified Contact Form Short Code

/*
Plugin Name: jQuery Contact Shortcode
Plugin URI: http://pippinsplugins.com/contact-shortcode/
Description: Adds a shortcode for displaying a jQuery Validated Contact Form
Version: 1.0
Author: Pippin Williamson
Author URI: http://184.173.226.218/~pippin 
*/
 
// plugin root folder
$cs_base_dir = WP_PLUGIN_URL . '/' . str_replace(basename( __FILE__), "" ,plugin_basename(__FILE__));

function pippin_shortcode_contact( $atts, $content = null)	{
 
	// gives access to the plugin's base directory
	global $cs_base_dir;
 
	extract( shortcode_atts( array(
      'email' => get_bloginfo('admin_email')
      ), $atts ) );
 
		$content .= '
		<script type="text/javascript"> 
			var $j = jQuery.noConflict();
			$j(window).load(function(){				
				$j("#contact-form").submit(function() {
				  // validate and process form here
					var str = $j(this).serialize();					 
					   $j.ajax({
					   type: "POST",
					   url: "' . $cs_base_dir . 'sendmail.php",
					   data: str,
					   success: function(msg){						
							$j("#note").ajaxComplete(function(event, request, settings)
							{ 
								if(msg == "OK") // Message Sent? Show the Thank You message and hide the form
								{
									result = "Your message has been sent. Thank you!";
									$j("#fields").hide();
								}
								else
								{
									result = msg;
								}								 
								$j(this).html(result);							 
							});					 
						}					 
					 });					 
					return false;
				});			
			});
		</script>';
 
                // now we put all of the HTML for the form into a PHP string
		$content .= '<div id="post-a-comment" class="clear">';
			$content .= '<div id="fields">';
				$content .= '<h4>Send A Message</h4>';
				$content .= '<form id="contact-form" action="">';
					$content .= '<input name="to_email" type="hidden" id="to_email" value="' . $email . '"/>';
					$content .= '<p>';
						$content .= '<input name="name" type="text" id="name"/>';
						$content .= '<label class="error" for="name">Name *</label>';
					$content .= '</p>';
					$content .= '<p>';
						$content .= '<input name="email" type="text" id="email"/>';
						$content .= '<label for="email">E-mail address *</label>';
					$content .= '</p>';
					$content .= '<p><textarea rows="" cols="" name="message"></textarea></p>';
					$content .= '<p><input type="submit" value="Submit" class="button" id="contact-submit" /></p>';
				$content .= '</form>';
			$content .= '</div><!--end fields-->';
			$content .= '<div id="note"></div> <!--notification area used by jQuery/Ajax -->';
		$content .= '</div>';
	return $content;
}

add_shortcode('contact', 'pippin_shortcode_contact');

wp_enqueue_script('jquery');

// allow us to use core wordpress functions
 
// make sure to replace this with the name of the plugin's root folder name
$plugin_name = 'contact_shortcode';
$oldURL = dirname(__FILE__);
$newURL = str_replace(DIRECTORY_SEPARATOR . 'wp-content' . DIRECTORY_SEPARATOR . 'plugins' . DIRECTORY_SEPARATOR . $plugin_name, '', $oldURL);
include($newURL . DIRECTORY_SEPARATOR . 'wp-load.php');

function ValidateEmail($email)
{
	/*
	(Name) Letters, Numbers, Dots, Hyphens and Underscores
	(@ sign)
	(Domain) (with possible subdomain(s) ).
	Contains only letters, numbers, dots and hyphens (up to 255 characters)
	(. sign)
	(Extension) Letters only (up to 10 (can be increased in the future) characters)
	*/
 
	$regex = '/([a-z0-9_.-]+)'. # name

	'@'. # at

	'([a-z0-9.-]+){2,255}'. # domain & possibly subdomains

	'.'. # period

	'([a-z]+){2,10}/i'; # domain extension 

	if($email == '') { 
		return false;
	}
	else {
		$eregi = preg_replace($regex, '', $email);
	}
 
	return empty($eregi) ? true : false;
}

$post = (!empty($_POST)) ? true : false;
 
if($post)
{
	$name = stripslashes($_POST['name']);
	$subject = 'Contact Form';
	$email = trim($_POST['email']);
	$to = trim($_POST['to_email']);
	$message = stripslashes($_POST['message']);
	$error = '';
 
	// Check name
 
	if(!$name)
	{
		$error .= 'Please enter your name.<br />';
	}
 
	// Check email
 
	if(!$email)
	{
		$error .= 'Please enter an e-mail address.<br />';
	}
 
	if($email && !ValidateEmail($email))
	{
		$error .= 'Please enter a valid e-mail address.<br />';
	}
 
	// Check message (length)
 
	if(!$message || strlen($message) < 15)
	{
		$error .= "Please enter your message. It should have at least 15 characters.<br />";
	}
 
	if(!$error) // send email
	{
		$mail = wp_mail($to, $subject, $message,
			 'From: '.$name.' <'.$email.'>\r\n'
			.'Reply-To: '.$email.'\r\n'
			.'X-Mailer: PHP/' . phpversion());
 
		if($mail)
		{
			echo 'OK';
		}
 
	}
	else
	{
		echo '<div class="notification_error">'.$error.'</div>'; // set up error div for jQuery/Ajax
	}
 
}

[contact email="youraddress"]