function ajax_update( url , this_div , vars , form ) {
	
	if ( $(this_div) ) {
	
		if ( form ) {
			vars += '&'+$(form).serialize();
		}
		var myAjax = new Ajax.Updater(
			this_div, 
			url, {
				method: 'post', 
				evalScripts: true,
				parameters: vars
			}
		);
	
	} else {
//		alert('div does not exist');
	}
	
}