html {  overflow-x:hidden;}  
body{ margin:0; padding:0;}  
#top{ width:100%; position:relative; height:50px;}  
#content{ width:980px; margin:0 auto; background:#999; height:500px; z-index:999; position:relative; padding-top:20px;}  
#wrapper{ height:50px; width:50%; position:relative; background:#09F; float:left;display:inline;}  
#w_2{ height:50px; width:50%; background:#F30; float:right; *position:absolute;}  
#menu{ position:absolute; top:-50px; left:0; height:50px; background:#F30; width:980px;display:inline;}  
 

<div id="top">
   <div id="wrapper"></div>
   <div id="w_2"></div>
</div>  
<div id="content">  
    <div id="menu"> 導航</div>  
    網站內容  
</div>