You can use this handy snippet of php code that I have come up with that will automatically redirect the user to the secure version of any page on the site if they visit the non secured version of the page.
<?php if((!(isset($_SERVER['HTTPS']))) || ($_SERVER['HTTPS'] == "") || ($_SERVER['HTTPS'] == "off"))header("Location: https://" . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF']); ?>
You would just add it to the top of any pages that you would like to only come up through https. Once the user is on the secure version of the site any relative links they click on will take them to the secure version of that page as well.