怎么样通过php在数据库抽象层简单使用PDO？

<?php
/**************************
@Filename: pdotest.php
@Content : PDO操作MySQL,Access（测试）
**************************/
if($_GET['db'] == 'mysql')
{
 $dns = 'mysql:host=localhost;dbname=test';
 $dbuser = 'root';
 $dbpass = 'root';
 $db = new PDO($dns,$dbuser,$dbpass);
}
else
{
 $db = new PDO("odbc:Driver={Microsoft Access Driver (*.mdb)};Dbq=".getcwd()."//test.mdb");
}
if($_POST['reg'])
{
 $db->exec("INSERT INTO t_user (name,email) VALUES ('".$_POST['name']."','".$_POST['email']."') ;");
 // header('Location:'.$_SERVER['PHP_SELF']);
 ?>
 <a href="pdotest.php">返回</a>
 <?
}
else
{
 $html = '
<div id="new">
 <form action="'.$_SERVER['REQUEST_URI'].'" method="post">
  Name: <input type="text" name="name" size="10" />
 Email: <input type="text" name="email" size="15" />
 <input type="submit" name="reg" value="Register" />
 </form>
</div>
';
 $re = $db->query("SELECT uid,name,email FROM t_user ORDER BY email ;");
 while($rs = $re->fetch())
 {
  $userlisthtml .= '
<tr><td>'.$rs['uid'].'</td><td>'.$rs['name'].'</td><td>'.$rs['email'].'</td></tr>';
 }
 $html .= '
<div id="list">
 <table border="1">
 <caption>User List</caption>
 <thead>
  <tr><th>ID</th><th>Name</th><th>Email</th></tr>
 </thead>
 <tbody>'.$userlisthtml.'
 </tbody>
 </table>
</div>
';
}
echo $html;
?>