var http = getHTTPObject();

function getHTTPObject() {
	var xmlhttp;
	try {
		xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
	} catch (e) {
		try {
			xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
		} catch (E) {
			xmlhttp = false;
		}
	}

	if (!xmlhttp && typeof XMLHttpRequest != "undefined") {
		try {
			xmlhttp = new XMLHttpRequest();
		} catch (e) {
			xmlhttp = false;
		}
	}

	return xmlhttp;
}

/* Example
	http.open("GET", "salida?p_cod_rh=0000875309", true);
	http.setRequestHeader("If-Modified-Since", "Sat, 1 Jan 1900 00:00:00 GMT");
	http.onreadystatechange = handleHttpResponse;
	http.send(null);
*/