function ajax(url, parameters, callback, isGet) {
	var request;
	
	var parameterString = "";
	for (var param in parameters) {
		if (parameterString) parameterString += "&";
		parameterString += param + "=" + escape(parameters[param]);
	}

	if (isGet) url += "?" + parameterString;
	
	if (window.XMLHttpRequest) {
		request = new XMLHttpRequest();
	} else if (window.ActiveXObject) {
		request = new ActiveXObject("Microsoft.XMLHTTP");
	}
	
	if (!request) {
		return;
	}
	
	if (callback) {
		request.onreadystatechange = function() {
			if (request.readyState == 4) {
				callback(request.status == 200, request.responseText);
			}
		}
	}
	
	request.open(isGet ? "GET" : "POST", url, true);
	if (!isGet) request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
	request.setRequestHeader("X-Requested-With", "XMLHttpRequest");
	request.send(isGet ? null : parameterString);
}