function open_popup(url,width,height){
	
	if (width > screen.width)
		width = screen.width;
	if (height > screen.height)
		height = screen.height
	attributes = "width="+width+", height="+height;
	t = (screen.height - height) / 2;
	l = (screen.width - width) / 2;
	attributes += "toolbar=no, scrollbars=yes,top="+t+",left="+l;
	window.open(url,"image",attributes);
}