I think you answered your own question already. A tags.php file should work just fine. You can get the tag through the URL. So, just make your tags clickable with an A tag, and point it to the tags.php?tag=bookreview
$tag = $_GET['tag']; // tags.php?tag=php
$query = "SELECT * FROM tags WHERE name='$tag'"; // slightly different, you know what should be here
$result = mysql_query($query);
while ($row = mysql_fetch_assoc($result))
// output your data here.