function open_center(url, name, params, Wwidth, Wheight) {
	Swidth = screen.width;
	Sheight = screen.height;

	Wleft = (Swidth / 2) - (Wwidth / 2) - 8;
	Wtop = (Sheight / 2) - (Wheight / 2) - 20;

	params = params+",left="+Wleft+",top="+Wtop+",width="+Wwidth+",height="+Wheight;

	window.open(url, name, params);
}