if (parseInt(navigator.appVersion.substring(0,1))>=3) {

  but1_off = new Image();
  but1_off.src = "assets/home_on1.jpg";
  but1_on = new Image();
  but1_on.src = "assets/home_off1.jpg";

  but2_off = new Image();
  but2_off.src = "assets/info_on.jpg";
  but2_on = new Image();
  but2_on.src = "assets/info_off.jpg";

  but3_off = new Image();
  but3_off.src = "assets/contact_on.jpg";
  but3_on = new Image();
  but3_on.src = "assets/contact_off.jpg";

}

function muis(imgDocID,imgObjName) {
  if (parseInt(navigator.appVersion.substring(0,1)) >= 3)
    document.images[imgDocID].src = eval(imgObjName + ".src") 
}