导出到EXCEL的数据的乱码?

<?php
header("Content-type:application/vnd.ms-excel");
header("Content-Disposition:filename=books.xls");
?>
<html xmlns:o="urn:schemas-microsoft-com:office:office"
xmlns:x="urn:schemas-microsoft-com:office:excel"
xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv=Content-Type content="text/html; charset=big5">
</head>
<body>
<?
...
?>