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

function SimpleSwapSetup()
{
  var x = document.getElementsByTagName("img");
  for (var i = 0; i < x.length; i++)
  {
    var oversrc = x[i].getAttribute("oversrc");
    if (!oversrc) continue;
      
    // preload image
    // comment the next two lines to disable image pre-loading
    x[i].oversrc_img = new Image();
    x[i].oversrc_img.src = oversrc;
    // set event handlers
    x[i].onmouseover = new Function("SimpleSwap(this, 'oversrc');");
    x[i].onmouseout = new Function("SimpleSwap(this);");
    // save original src
    x[i].setAttribute("origsrc", x[i].src);
  }
}

var PreSimpleSwapOnload = (window.onload) ? window.onload : function(){};
window.onload = function() { PreSimpleSwapOnload(); SimpleSwapSetup(); }