$(document).ready(function(){
  var bigHref = $('#placeholder').attr('src');  // save the src of the main image
  $('div.thumb a').click(function() { return false; }); // don't do anything if you click the thumbnail
  $('div.thumb a').hover(function(){
    var imgHref = $(this).attr('href');  // get the src of the thumbnail
    $('#placeholder').attr('src',imgHref);  // set src attribute of main photo
    $('#desc').text($(this).attr('title')); // set the caption
  },
  function(){    // onmouseout, don't do anything
  });
});