var http_request = false;
function makePOSTRequest(url,requestString,callback_function) {
//  url = URL + '/' + url;
  http_request = false;
  if (window.XMLHttpRequest) { // Mozilla, Safari,...
     http_request = new XMLHttpRequest();
     if (http_request.overrideMimeType) {
     	// set type accordingly to anticipated content type
        http_request.overrideMimeType('text/xml');
        //http_request.overrideMimeType('text/html');
     }
  } 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('Cannot create XMLHTTP instance');
     return false;
   
  }
  
  http_request.onreadystatechange = function() {
               	if(http_request.readyState == 4)
               		{
     							if (http_request.status == 200) {
        						eval(callback_function + '(http_request.responseXML)');
                  }
                 else
                 	alert('There was a problem with the request.(Code: ' + http_request.status + ')'); 
          		}
          }
  http_request.open('POST', url, true);
  http_request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  http_request.setRequestHeader("Connection", "close");
  http_request.send(requestString);
}