Login and back from non-forum pages

[Gregory]

Hi, I've read this thread but it hasn't helped me. (maybe pointed me in the right direction though) http://www.simplemachines.org/community/index.php?topic=27475.msg228552#msg228552


I have non-forum pages that load the ssi file and know if the visitor is logged into the forum or not.
If they're not logged in I want to show them a username/password form that they can use to login but then be returned to the non-forum page.

So I need to set $_SESSION['login_url'] = 'http://mysite.com/returned-page.php'; but before or after the other stuff?
And what other stuff do I need to use to attempt to log them in?