Css Filter

http://www.cnblogs.com/hedonister/archive/2005/12/21/302062.html

如果要在js里用
以下面的方式：

        <script>
        function mov(obj)
        {
          obj.style.filter="progid:DXImageTransform.Microsoft.Alpha(opacity=100)";
        }
        function mou(obj)
        {
          obj.style.filter="progid:DXImageTransform.Microsoft.Alpha(opacity=80)";
        }
        </script>

      <div onmousemove="mov(this)" onmouseleave="mou(this)">
            <a href="#"><img src="image/Folder-Sites.png" /><br/><span>TestTest</span></a>
        </div>