高手，我有问题！！！！急！！！！

大家帮我看下这个代码；

<?php
//session_start();
$host="localhost";
$username="root";
$password="123456";
$datebase="msg";
$conn=mysql_connect($host,$username,$password);
mysql_select_db($datebase,$conn);
mysql_query("SET NAMES 'GBK'");
$useradmin=$_POST['useradmin'];
$userpwd=md5($_POST['userpwd']);
$sql="select useradmin,userpwd from user where useradmin='$useradmin' and userpwd='$userpwd'";
$rs=mysql_query($sql);
$array=mysql_num_rows($rs);
if (!empty($array)){
if ($array['useradmin']==$useradmin){
  session_start();
  $_SESSION['admin']=ture;
}
else {
  echo "用户密码错误！";
}
}
else {
echo "用户密码错误！";
}
?>
<table width="100%" height="100%" border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
<form action="login.php" method="post"><td align="center" valign="middle"><table width="400" border="0" cellpadding="5" cellspacing="1" class="tablebg">
<tr class="tdbg">
<td colspan="2"><div align="center">Administrators Login</div></td>
</tr>
<tr class="tdbg">
<td><div align="center">Username</div></td>
<td><div align="center">
<input name="useradmin" type="text" id="username">
</div></td>
</tr>
<tr class="tdbg">
<td><div align="center">Password</div></td>
<td><div align="center">
<input name="password" type="userpwd" id="password">
</div></td>
</tr>
<tr class="tdbg">
<td colspan="2"><div align="center">
<input type="submit" name="Submit" value="Submit">
<input type="reset" name="Submit2" value="Clear">
</div></td>
</tr>
</table></td></form>
</tr>
</table>

   请问下，我这段代码在设置COOKIE对不？  我想再弄个设置保存用户名时间的功能，应该怎么加代码，是在同一个页面吗？请帮我写下具体的代码和过程啥！

设置cookie用setcookie函数
详细用法：
http://www.phpfans.net/bbs/PHPfunction.php?function=setcookie