function canManipulateImages() {
   if (document.images)
      return true;
   else
      return false;
}

function preLoadImage(imageURL) {
   if (gImageCapableBrowser) {
      image = new Image();
      image.src = imageURL;
      return image;
   }
}

function chgImg(buttonName,sourceImage) {
   if (gImageCapableBrowser) {
      document [buttonName].src = sourceImage.src;
      return true;
   }
}

gImageCapableBrowser = canManipulateImages();

about_off = preLoadImage("images/about1.gif");
about_on = preLoadImage("images/about2.gif");

dist_off = preLoadImage("images/dist1.gif");
dist_on = preLoadImage("images/dist2.gif");

prod_off = preLoadImage("images/prod1.gif");
prod_on = preLoadImage("images/prod2.gif");

feed_off = preLoadImage("images/feed1.gif");
feed_on = preLoadImage("images/feed2.gif");