jquery实现导航固定顶部的效果，仿蘑菇街的，感觉还不错，需要的朋友可以参考下
<!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>无标题文档</title>
<script type="text/javascript" src="js/jquery-1.4.2.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
var headHeight=$(".header").height()+10;
var nav=$(".nav");
$(window).scroll(function(){
if($(this).scrollTop()>headHeight){
nav.addClass("navFix");
}
else{
nav.removeClass("navFix");
}
})
})
</script>
<style type="text/css">
*{ margin:0; padding:0;}
body{ _background-attachment:fixed; _background-image:url(about:blank);} //实现ie6不支持fixed方法
.header{ width:1000px; height:60px; margin:0 auto; text-align:center;}
.nav{ border:1px solid #ccc; border-radius:5px; overflow:hidden; height:30px; width:1000px; margin:10px auto; background:#fff;}
.nav li{ float:left; padding:0 10px; height:30px; line-height:30px;}
.nav li a{ text-decoration:none; color:#0CF;}
.nav li a:hover{ color:#000; text-decoration:underline;}
.nav ul{ list-style:none;}
.navFix{ position:fixed; left:0; top:0; _position:absolute; top:expression((offsetParent.scrollTop)+0); z-index:2;} //实现ie6不支持fixed方法
.content{ width:1000px; margin:10px auto;}
</style>
</head>
<body>
<div class="header">
<h1>导航固定在页面顶部测试</h1>
</div>
<div class="nav">
<ul>
<li><a href="">首页</a></li>
<li><a href="">蓝枫前端</a></li>
<li><a href="">蓝枫前端</a></li>
<li><a href="">蓝枫前端</a></li>
<li><a href="">蓝枫前端</a></li>
<li><a href="">蓝枫前端</a></li>
<li><a href="">蓝枫前端</a></li>
<li><a href="">蓝枫前端</a></li>
</ul>
</div>
<div class="content">
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</div>
</body>
</html>
