function ShowPageVar(winUrl,winName,w,h,top,left)  {
  left = (screen.width) ? (screen.width-w)/2 : 0;
  top = (screen.height) ? (screen.height-h)/2 : 0;
  winFeatures='width='+w+',height='+h+',titlebar=0,resizable=0,top='+top+',left='+left;
  window.open(winUrl,winName,winFeatures);
}

<!-- ,screenX,screenY
<!-- +',screenX='+screenX+',screenY='+screenY