为什么在IE8下不能居中???

<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Web.master.cs" Inherits="Company.Web" %><!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 runat="server">
    <title>webname</title>
    <asp:ContentPlaceHolder ID="head" runat="server">
    </asp:ContentPlaceHolder>
</head>
<body style="margin:0px;">
    <form id="form1" runat="server">
    <div style="text-align:center; width:960px;">
        
        <table id="__01" width="960" border="0" cellpadding="0" cellspacing="0" style="height:814px;">
            ......
        </table>
        
    </div>
    </form>
</body>
</html>刚装的win7,但这个页面不能居中,之前在XP的IE6下是正常的,为什么会这样? 如何解决,谢谢.