这是一个很基础的问题。主要还是因为IE跟firefox不兼容的问题。以下是我帮你改好的。仔细看看吧。希望对有帮助。别外以后做网页还是要带上头部w3c的申明。祝你学习愉快!!
<!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>div居中</title>
<style type="text/css">
<!--
body{text-align:center;}
.juzhong {text-align:left; margin:0px auto; width:800px; height:200px; border:1px solid #ccc;}
-->
</style>
</head>
<body>
<div class="juzhong">just have a test</div>
</body>
</html>