function PopUp(strFile, nWidth, nHeight)
{
    if((typeof WindowPopUp != "undefined") && (WindowPopUp != null))
        WindowPopUp.close();

    WindowPopUp = window.open("popup.php?file="+strFile+"&height="+nHeight+"&width="+nWidth, "popup", "left="+((screen.width-nWidth)/2)+", top="+((screen.height-nHeight)/2)+", width="+nWidth+", height="+nHeight);
    if(WindowPopUp != null)
        WindowPopUp.focus();
}