if(document.images) {
  img1on = new Image();
  img1on.src = "img/menu/main_on.gif";
  img1off = new Image();
  img1off.src = "img/menu/main_off.gif";

  img2on = new Image();
  img2on.src = "img/menu/galleries_on.gif";
  img2off = new Image();
  img2off.src = "img/menu/galleries_off.gif";

  img3on = new Image();
  img3on.src = "img/menu/info_on.gif";
  img3off = new Image();
  img3off.src = "img/menu/info_off.gif";
}

function imgOn(imgName) {
  if(document.images)     {
    document[imgName].src = eval(imgName + "on.src");
  }
}

function imgOff(imgName) {
  if(document.images)      {
    document[imgName].src = eval(imgName + "off.src");
  }
}