1、getElementById('"Layer5') 括號裏多了個雙引號
2、js無關閉標簽，</script>
給妳整個更簡單的啊：
<script type="text/javascript" src="/mei02_ku/mei02_ku.js"></script>
<script type="text/javascript">
<!--
$(document).ready(function(){
$(":input[type='submit']").click(function(){$("#Layer3").css({"display":"none"});$("#Layer5").css({"display":""});})
$(":input[type='button']").click(function(){$("#Layer5").css({"display":"none"});$("#Layer3").css({"display":""});})
})
//-->
</script>
</head>
<body>
<div id="Layer3">
<form id="form1" name="form1" method="post" action="">
<table width="745" border="1">
<tr>
<td width="179"><p>用戶名 <br />
<br />
</p></td>
<td width="550"><label>
<input type="text" name="textfield" />
</label></td>
</tr>
<tr>
<td>性別</td>
<td><label>
<input type="radio" name="radiobutton" value="radiobutton" />
男
<input type="radio" name="radiobutton" value="radiobutton" />
女
</label></td>
</tr>
<tr>
<td>生日</td>
<td><label>
<select name="select">
</select>
年
<select name="select2">
</select>
月
<select name="select3">
</select>
日
</label></td>
</tr>
<tr>
<td>頭像文件</td>
<td><label>
<input type="image" name="imageField" src="image/bankuai/a.jpg" />
</label></td>
</tr>
<tr>
<td>註冊日期</td>
<td>xxxx</td>
</tr>
<tr>
<td>最後壹次登錄時間</td>
<td>xxxx</td>
</tr>
<tr>
<td>登錄次數</td>
<td>xxx</td>
</tr>
<tr>
<td>用戶積分</td>
<td>xxx</td>
</tr>
<tr>
<td>個性簽名</td>
<td><input type="text" name="textfield2" /></td>
</tr>
<tr>
<td></td>
<td><input name="修改" type="submit" value="修改" />
<input name="修改" type="reset" value="重置" /></td>
</tr>
</table>
</form>
</div>
<div id="Layer5">
<table width="745" border="1">
<tr>
<td width="179" height="26"><p>用戶名 <br />
<br />
</p></td>
<td width="550"><label>a</label></td>
</tr>
<tr>
<td height="25">性別</td>
<td><label>b</label></td>
</tr>
<tr>
<td>生日</td>
<td><label>
<select name="select4">
</select>
年
<select name="select4">
</select>
月
<select name="select4">
</select>
日 </label></td>
</tr>
<tr>
<td>頭像文件</td>
<td><label>
<input type="image" name="imageField2" src="image/bankuai/a.jpg" />
</label></td>
</tr>
<tr>
<td>註冊日期</td>
<td> </td>
</tr>
<tr>
<td>最後壹次登錄時間</td>
<td> </td>
</tr>
<tr>
<td>登錄次數</td>
<td> </td>
</tr>
<tr>
<td>用戶積分</td>
<td> </td>
</tr>
<tr>
<td>個性簽名</td>
<td> </td>
</tr>
<tr>
<td></td>
<td><input name="修改" type="button" value="修改個人信息" /></td>
</tr>
</table>
</div>