if (parseInt(navigator.appVersion.substring(0,1))>=3) { // 3.0 or greater.

home_on = new Image();
home_off = new Image();
home_off.src = 'images_base/header_nav_in_1_off.jpg';
home_on.src = 'images_base/header_nav_in_1_on.jpg';

}

function on(image) {
  if (parseInt(navigator.appVersion.substring(0,1))>=3) { // 3.0 or greater.
      imagesrc = eval(image + '_on.src');
      document[image].src = imagesrc;
  }
}

function off(image) {
  if (parseInt(navigator.appVersion.substring(0,1))>=3) { // 3.0 or greater.
      imagesrc = eval(image + "_off.src");
      document[image].src = imagesrc;
 }
}