function cargarPagina(url,contenedor){
    AJAX(url, contenedor, null, true);
}

function nuevoAjax(){
     var xmlhttp=false;
     try {
         xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
     } catch (e) {
            try {
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (E) {
                    xmlhttp = false;
            }
        }

    if (!xmlhttp && typeof XMLHttpRequest!='undefined') {
        xmlhttp = new XMLHttpRequest();
    }
    return xmlhttp;
}


function AJAX(url,contenedor,variables,abrir){
    var contenedor;
    contenedor = document.getElementById(contenedor);
    ajax=nuevoAjax();
    ajax.open("POST", url ,abrir);
    ajax.onreadystatechange=function() {
            if (ajax.readyState==4) {
                  contenedor.innerHTML = ajax.responseText;
            }
    }
    ajax.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    ajax.send(variables);
}