$(document).ready(function() {
  $('img#the_img').each(function() {
    var loader = new Image();
    loader.src = this.src.replace(/thumbs/, 'images');
  }).get(0).src = $('div.thb img').get(0).src.replace(/thumbs/, 'images');
  $('div.thb img').mouseover(function() {
    $('img#the_img').get(0).src = this.src.replace(/thumbs/, 'images');
  })
});