$(document).ready(function(){
  setTimeout('progressImage()', 4000);
});

function progressImage()
{
  var currImg = $('#header img');
  img = new Image();
  img.onload = function(){
    newImg = $('<img src="' + this.src + '" />');
    newImg.css({ display: 'none', zIndex: '3' });
    $('#header').append(newImg);
    newImg.fadeIn(1000, function(){
      currImg.remove();
      setTimeout('progressImage()', 4000);
    });
  };
  currImgNum = currImg.attr('src').substr(currImg.attr('src').length - 5,1);
  img.src = currImg.attr('src').replace(currImgNum, (currImgNum == 3) ? 1 : parseInt(currImgNum) + 1);
}