function open_new_window(url, window_name) {
    var iMyWidth;
    var iMyHeight;
    //half the screen width minus half the new window width (plus 5 pixel borders).
    iMyWidth = (window.screen.width / 2) - (450 + 10);
    //half the screen height minus half the new window height (plus title and status bars).
    iMyHeight = (window.screen.height / 2) - (300 + 50);
    //Open the window.
    new_window = window.open(url, window_name, 'toolbar=0,menubar=0,resizable=yes,dependent=0,status=0,width=900,height=600,scrollbars,left=' + iMyWidth + ',top=' + iMyHeight);
    if (window.focus) { new_window.focus() };
}