function popupWindow(url,width,height) {
   winName = "extChild";
   xPos = (self.screen.width - width) / 2 ;
   yPos = (self.screen.height - height) / 2 ;
   if (!width) width = 600;
   if (!height) height = 450;
   args = "width=" + width + "," + "height=" + height + "," + "location=0," + "menubar=0," + "resizable=1," + "scrollbars=1,";
   args = args + "status=1," + "titlebar=0," + "toolbar=0," + "hotkeys=0," + "screenx=" + xPos + "," + "screeny=" + yPos + ",";
   args = args + "left=" + xPos + "," + "top=" + yPos;
   extChild = window.open(url,winName,args);
   if (!extChild.closed) extChild.focus();
}