function popup(url,windowname,width,height,features)
{
width=(width)?width:screen.width/2;
height=(height)?height:screen.height/2;
var screenX = (screen.width/2 - width/2);
var screenY = (screen.height/2 - height/2);
var features= "width=" + width + ",height=" + height +",scrollbars=yes,status=yes";
features += ",screenX=" + screenX + ",left=" + screenX;
features += ",screenY=" + screenY + ",top=" + screenY;

var mywin=window.open(url, windowname, features);
if (mywin)
mywin.focus();
return mywin;
}