var http_request = false;
function makeRequest(url, formid) {
	 
	
		  var Formulario = formid;
          var longitudFormulario = Formulario.elements.length;
          var cadenaFormulario = ""
          var sepCampos
          sepCampos = ""
          for (var i=0; i <= Formulario.elements.length-1;i++) {
			  cadenaFormulario += sepCampos+Formulario.elements[i].name+'='+encodeURI(Formulario.elements[i].value);
			  sepCampos="&";
			 
		  }
	
        http_request = false;

        if (window.XMLHttpRequest) { // Mozilla, Safari,...
            http_request = new XMLHttpRequest();
            if (http_request.overrideMimeType) {
                http_request.overrideMimeType('text/xml');
                // Ver nota sobre esta linea al final
            }
        } else if (window.ActiveXObject) { // IE
            try {
                http_request = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    http_request = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e) {}
            }
        }

        if (!http_request) {
            alert('Falla :( No es posible crear una instancia XMLHTTP');
            return false;
        }
        http_request.onreadystatechange = alertContents;
        http_request.open('POST', url, true);
		http_request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=iso-8859-1');
        http_request.send(cadenaFormulario);
		

    }