function popupWindow(SeitenURL, window_width, window_height) {
	var top_margin = (screen.height - window_height) / 2;
	var left_margin = (screen.width - window_width) / 2;
	newWindow = window.open(SeitenURL, "newWindow", "width=" + window_width
				+ ",height=" + window_height
				+ ",scrollbars");
	

	newWindow.moveTo(left_margin,top_margin);
	newWindow.resizeTo(window_width, window_height);
	newWindow.focus();
}