Since his site is built in PHP, have him check out the PHP <a href="http://us2.php.net/manual/en/function.mail.php" target="_blank">mail()</a> function as he could use it to easily send e-mails to anyone on a list whenever something on the site is updated.

I wish I could give more assistance than this, but I'm not sure what would be the best thing to do without seeing exactly how the site runs.