$(document).ready(function(){

  // bind to the hover event on each li (list item)
  $("div#features li").each(function(){
    var feature = $(this);
    // this binds to the mouse over event
    feature.bind("mouseover", function(){
      if($('img#feature_image').attr('src')!='images/'+feature.attr("class")+'.jpg'){
        $('img#feature_image').fadeOut("fast", function(){
          $(this).attr('src', 'images/'+feature.attr("class")+'.jpg').fadeIn("fast");
        })
      };
    });
  });
  
});