var request = false;
try {
	request = new XMLHttpRequest();
} 
catch (trymicrosoft) {
	try {
		request = new ActiveXObject('Msxml2.XMLHTTP');
	} 
	catch (othermicrosoft) {
		try {
			request = new ActiveXObject('Microsoft.XMLHTTP');
		} 
		catch (failed) {
			request = false;
		}  
	}
}
if (!request) alert('Ошибка инициализации XMLHttpRequest!');