function createXMLHttpRequest() {
	var xmlHttp = false;
	if (window.XMLHttpRequest) { // Mozilla, Safari,...
		xmlHttp = new XMLHttpRequest();
		if (xmlHttp.overrideMimeType){
			xmlHttp.overrideMimeType('text/xml');
		}
	}else if (window.ActiveXObject){ // IE
		try{
			 xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
		}catch(E) {
			 try{
			 	xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
			 }catch(E){}
		}
	}
	if (!xmlHttp) {
		alert('Giving up :( Cannot create an XMLHTTP instance');
		return false;
	}
	return xmlHttp;
}

function httpRequestByPost(xmlHttp,u,postData) {
	xmlHttp.open('POST', u, true);
   	xmlHttp.setRequestHeader("content-length",postData.length);
   	xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded;charset=UTF-8");
   	xmlHttp.setRequestHeader('Cache-Control', 'no-cache');
   	xmlHttp.setRequestHeader('Pragma', 'no-cache');
   	xmlHttp.setRequestHeader("If-Modified-Since","0");
   	xmlHttp.send(postData);
}

function httpRequestByGet(xmlHttp,u) {
	xmlHttp.open('GET', u, true);
	xmlHttp.setRequestHeader('Cache-Control', 'no-cache');
   	xmlHttp.setRequestHeader('Pragma', 'no-cache');
   	xmlHttp.setRequestHeader("If-Modified-Since","0");
	xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded;charset=UTF-8");
   	xmlHttp.send(null);
}