function popup(url, title, W, H, features){
	var X = Math.ceil((window.screen.availWidth - W) / 2);
	var Y = Math.ceil((window.screen.availHeight - H) / 2);
	features = "width=" + W + ", height=" + H + ", left=" + X + ", top=" + Y + ", " + features;
	window.open(url, title, features);
}