newbie has a question

From: nome (nome_at_poczta.wp.pl)
Date: 02/28/05 

Date: Mon, 28 Feb 2005 12:04:10 +0100

hi,
i'm really beginner in php programming so please give me an advice. is the
script safe or not?

<?php
  $path = "directory/";
  $extension = ".htm";

  if ( preg_match("#^[a-z0-9_]+$#i",$page) ){
  $id = $path.$page.$extension;
  include($id);

  }

echo"
<HTML><BODY>$id</BODY></HTML>";

?>

best regards
nome