$(function () {
  if ($.browser.msie && $.browser.version < 7) return;
  
  $('#navigation li')
    .removeClass('highlight')
    .find('a')
    .append('<span class="hover" />').each(function () {
      var $span = $('> span.hover', this).css('opacity', 0);
      $(this).hover(function () {
        // on hover
        
        // stop any animations currently running, and fade to opacity: 1
        $span.stop().fadeTo(600, 1);
      }, function () {
        // off hover
        
        // again, stop any animations currently running, and fade out
        $span.stop().fadeTo(800, 0);
      });
    });
});