=>代码

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
 <head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
  <title>样式</title>
     <style type="text/css">
   #out{
    width: 90%;
    min-width: 764px;
    margin: auto; /*使out居中*/
   }
  
   #header{
    height: 120px;
    background-color:#669966;
   }
   
   #left_menu{
    float: left;
    height: 380px;
    width: 20%;
    background-color:#CCCCCC;
   }
   
   #right_main{
    float: right;
    height: 380px;
    width: 80%;
    background-color:#CCCCFF;
   }
   
   #footer{
    height: 80px;
    clear: all; /*清除左右两边浮动*/
    background-color:#666666;
   }
  </style>
 </head> 
  
 
   <body>
  <div id="out">
      <div id="header">
          头部
         </div>
         <div id="left_menu">
          左边菜单
         </div>
         <div id="right_main">
          主体内容
         </div>
         <div id="footer">
          尾部
         </div>
     </div>
 </body>
 </html>