How to add icons for Drupal 6 menus?
Try the css way

li.menu-mlid-600 &gt; a {
    background-image: url('../images/my_icon.png');
    height: 150px;
    width: 200px;
    text-indent: -9999px;
    display: block;
}


But there are other ways. Google it. Here is another way:

How to use images for menu items in Drupal with a simple preprocessing function