function popup(filename, w, h) {
	win = null;
	if (window.screen) {
		aw = screen.availWidth;
		ah = screen.availHeight;
	} else {
		aw = 800;
		ah = 600;
	}

	opt = "width=" + w + ",height=" + h + ",left="
	+ (aw-w)/2 + ",top="
	+ (ah-h)/2
	+ ",toolbar=no,location=no,directories=no,"
	+ "status=no,menubar=no,"
	+ "scrollbars=yes,resizable=no";

	win = window.open(filename, '', opt);
}