if (document.images) {
  // preload pictures
  menucOff = new Image();
  menucOff.src = "images/menuclosed.gif";
  menucOn = new Image();
  menucOn.src = "images/menuclosedhover.gif";

  menuoOff = new Image();
  menuoOff.src = "images/menuopen.gif";
  menuoOn = new Image();
  menuoOn.src = "images/menuopenhover.gif";
}

function hoverOn(thisName) { 
  if (document.images) {
    picName = eval(String(thisName).substring(0,5) + "On.src");
    document.images[thisName].src = picName;
  }
}

function hoverOff(thisName) {
  if (document.images) {
    picName = eval(String(thisName).substring(0,5) + "Off.src");
    document.images[thisName].src = picName;
  } 
}