ver_hover = 
  (((navigator.appName == "Netscape") && 
  (parseInt(navigator.appVersion) >= 3 )) || 
  ((navigator.appName == "Microsoft Internet Explorer") && 
  (parseInt(navigator.appVersion) >= 4 ))); 


if (ver_hover && document.images)
  {
   var indietroon  = new Image()
   indietroon.src  = "down_on.gif"
   var indietrooff = new Image()
   indietrooff.src = "down_off.gif"

   var avantion  = new Image()
   avantion.src  = "up_on.gif"
   var avantioff = new Image()
   avantioff.src = "up_off.gif"

   var indiceon  = new Image()
   indiceon.src  = "index_on.gif"
   var indiceoff = new Image()
   indiceoff.src = "index_off.gif"

   var homeon  = new Image()
   homeon.src  = "home_on.gif"
   homeoff     = new Image()
   homeoff.src = "home_off.gif"
  }

          
function on(imgName){
 if (ver_hover && document.images)
   document[imgName].src = eval(imgName + 'on.src')
}
          

function off(imgName) {
 if (ver_hover && document.images)
   document[imgName].src = eval(imgName + 'off.src')
}