function open_preview_window( title, url, width, height) {
	var wnd_height = ((height) ? height : 600)+50;
	var wnd_width = ((width) ? width : 500)+30;
	wnd_width = ( wnd_width < 250 ) ? 250 : wnd_width;
	var wnd_left = ( screen.width - width ) / 2;
	var wnd_top = ( screen.height - height ) / 2;

	var wpopup = window.open( url, "", "location=no,menubar=no,resizable=1,personalbar=no,scrollbars=yes,status=no,toolbar=no,width="+wnd_width+",height="+wnd_height+",left="+wnd_left+",top="+wnd_top);
	wpopup.resizeTo(wnd_width, wnd_height);
	wpopup.document.close();
	wpopup.focus();
	return false;
}