You can build in more checks, and can fully-utilize the language file by pulling the text out of the template and into the lang file using constants the same way it's doing it now.

You would do that for the error messages too from header_php.php and swap actual messages for constants.

Also, in the template file, in some places I used Zen functions, in other places I just used what you already had. You might want to continue using Zen functions, and maybe even put in more places where it auto-displays what the user had entered in case they get an error message.... by using the $_POST info... etc...

Hope it helps.