function swapImage(el,which)
{
  el.src=el.getAttribute(which||"origsrc");
}

function swapImageSetup()
{
  var x = document.getElementsByTagName("img");
  for (var i=0; i< x.length; i++)
  {
    var str = x[i].src
    var index = str.indexOf("button-off");
    if (index <= 0)
      continue;
    var str2 = str.substring(0, index) + "button-over" + str.substring(index + 10);
    x[i].setAttribute("oversrc", str2);
    x[i].oversrc_img = new Image();
    x[i].oversrc_img.src = str2;
    x[i].onmouseover = new Function("swapImage(this,'oversrc');");
    x[i].onmouseout = new Function("swapImage(this);");
    x[i].setAttribute("origsrc", str);
  }
}

window.onload = swapImageSetup;