After opening a lightbox with thickbox: see http://jquery.com/demo/thickbox/

You can close the lightbox and have an href link open a url in the parent window:

<a href=\"javascript:parent.location.href='https://alum.mit.edu/register.vm';javascript:top.tb_remove();\">Register for an Infinite Connection account.</a>

Also to have a form and click submit but close the lightbox and have the form submit to the parent page use this code.

<?php
$output .= "<form action=\"https://alum.mit.edu/AlumVerifier.dyn\" target=\"_parent\" accept-charset=\"UTF-8\" method=\"post\" id=\"user-login-form\">
?>
</pre>

this took me an hour or two to figure out, so you're welcome :)