function popup(url, width, height) {
	var wh = height;
	var ww = width;
	
	var sh = screen.height;
	var sw = screen.width;
	
	var pl = (sw/2)-(ww/2);
	var pt = (sh/2)-(wh/2);
	
	newwindow = window.open(url,'chat_window','toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=1,width='+ww+',height='+wh+',left='+pl+',top='+pt);
	if (window.focus) {newwindow.focus()}
	return false;
}