function popUp(fileName, popUpWidth, popUpHeight) {
   margeLeft = (screen.width - popUpWidth) / 2;
   margeTop = (screen.height - popUpHeight) / 2;
   
   parameterString = "width=" + popUpWidth + ",height=" + popUpHeight + ",left=" + margeLeft + ",top=" + margeTop + ",scrollbars=no";
   popWindow = window.open(fileName, "_blank", parameterString);
   popWindow.focus();
}