$('bsub').observe('click', function(e) {

	var errors = [];
	
	// make sure required fields are filled in ...
	if ($F('first_name') == '') {
		errors.push('<li>You must enter your first name!</li>');
	}
	if ($F('last_name') == '') {
		errors.push('<li>You must enter your last name!</li>');
	}
	if ($F('email') == '') {
		errors.push('<li>You must enter your email address!</li>');
	}
	if ($F('zip') == '') {
		errors.push('<li>You must enter your ZIP code!</li>');
	}
	
	if (errors.length > 0) {
		open_message_modal('Error!', "I'm sorry, but we were unable to process your submission.<ul>"+errors.join("\n")+"</ul>");
		Event.stop(e);
		return false;
	} else {
		$('f').submit();
	}	
	
});