var images = document.getElementById('menu').getElementsByTagName('img');
for(x=0;x<images.length;x++)
{
  if(images[x].src.search('_f2.gif')<0)
  {
    images[x].onmousemove = function() { swap_image(this); };
    images[x].onmouseout  = function() { restore_image(this); };
  }
}
    
function restore_image(img)
{
  if(img.src.search('_f2.gif')>0)
    img.src = img.src.replace('_f2.gif','.gif');      
}//end restore_image
    
function swap_image(img)
{    
  if(img.src.search('_f2.gif')<0)
   img.src = img.src.replace('.gif','_f2.gif');
}//end swap_image