#nav{ background:url(nav-bg.jpg) repeat-x; height:50px; width:100%;}

#nav ul li{ float:left; height:50px; line-height:50px; display:block; width:99px; text-align:center;}

#nav ul li a{ color:#FFF; font-size:16px;}

#nav ul li a:hover, .currclass{ color:#333; background:url(nav-hover.jpg) repeat-x; width:99px; display:block;}

<div id="nav">

   <ul>

      <li class="currclass"><a href="/">首 页</a></li>

      <li><a href="/Item/list.asp?id=2">公司简介</a></li>

      <li><a href="/Item/list.asp?id=3">产品展示</a></li>

   </ul>

</div>