old_button = '';

function showbutton (index, imgurl)
{
  if (old_button != ''){
    hidebutton(old_button);
  } 

  document.getElementById('startpage-button-'+ index).className = 'startpage-button-act';
  //document.getElementById('startpage-box-text-'+ index).style.display = "";
  document.images['startpagebox'].src = imgurl;
  old_button = index;
}

function hidebutton (index)
{
  document.getElementById('startpage-button-'+ index).className = 'startpage-button';
  //document.getElementById('startpage-box-text-'+ index).style.display = "none";
}