/**
 * @author Diego
 */
  function crearInstancia(){
                var XMLHttp = null;
                if (window.XMLHttpRequest) {
                
                    return new XMLHttpRequest();
                }
                else 
                    if (window.ActiveXObject) {
                    
                        var versiones = ["Msxml2.XMLHTTP.7.0", "Msxml2.XMLHTTP.6.0", "Msxml2.XMLHTTP.5.0", "Msxml2.XMLHTTP.4.0", "Msxml2.XMLHTTP.3.0", "Msxml2.XMLHTTP", "Microsoft.XMLHTTP"];
                        for (var i = 0; i < versiones.length; i++) {
                            try {
                                XMLHttp = new ActiveXObject(versiones[i]);
                                if (XMLHttp) {
                                    return XMLHttp;
                                    break;
                                }
                                else 
                                    if (!XMLHttp) {
                                        alert('No se pudo crear la instancia');
                                    }
                            } 
                            catch (e) {
                            };
                                        }
                    }
            }