function ajax(url, id_contenedor){
	var pagina_requerida = false;
	if (window.XMLHttpRequest)    {
		pagina_requerida = new XMLHttpRequest ();// Si es Mozilla
	}
	else if (window.ActiveXObject){	// Si es IE
		try{
			pagina_requerida = new ActiveXObject ("Msxml2.XMLHTTP");
		}
		catch (e){	// Version antigua IE
			try{
				pagina_requerida = new ActiveXObject ("Microsoft.XMLHTTP");
			}
			catch (e){}
        }
	} 
	else
		return false;

    pagina_requerida.onreadystatechange = function (){cargarpagina (pagina_requerida, id_contenedor);}
    pagina_requerida.open ('GET', url, true);
    pagina_requerida.send (null);
}
function cargarpagina(pagina_requerida, id_contenedor)
{
    if (pagina_requerida.readyState == 4 && (pagina_requerida.status == 200 || window.location.href.indexOf ("http") == - 1))
    document.getElementById (id_contenedor).innerHTML = pagina_requerida.responseText;
}