function createREQ() {
try {
     req = new XMLHttpRequest(); /* p.e. Firefox */
     } catch(err1) {
       try {
       req = new ActiveXObject('Msxml2.XMLHTTP'); /* algunas versiones IE */
       } catch (err2) {
         try {
         req = new ActiveXObject("Microsoft.XMLHTTP"); /* algunas versiones IE */
         } catch (err3) {
          req = false;
         }
       }
     }
     return req;
}
function requestGET(url, query, req) {
	myRand=parseInt(Math.random()*99999999);
	req.open("GET",url+'?'+'query'+'&rand='+myRand,true);
	req.send(null);
}
function requestPOST(url, query, req) {
	req.open("POST", url,true);
//	req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded ');
	req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8")
	req.send(query);
}
function doCallback(callback,item) {
	eval(callback + '(item)');
}

function doAjax(url,query,callback,reqtype,getxml) {
// crea la instancia del objeto XMLHTTPRequest 
	var myreq = createREQ();
	myreq.onreadystatechange = function() {
		if(myreq.readyState == 4) {
		   if(myreq.status == 200) {
			  var item = myreq.responseText;
			  if(getxml==1) {
				 item = myreq.responseXML;
			  }
			  doCallback(callback, item);
			}
		  }
	}
	if(reqtype=='post') {
		requestPOST(url,query,myreq);
	} else {
		requestGET(url,query,myreq);
	}
}