from my welcome to strongbox email:

"CUSTOMIZING THE LOGIN AND DENIED PAGES

The login page and the page shown when a log in
attempt is denied are both pain HTML files that you
can edit with any text editor to better suit the look
of your site. We don't suggest using a WYSIWYG such
as FrontPage because as these programs are designed
primarily for home use on amateur web sites they may
make changes to your pages which aren't desired on a
professional site. Dreamweaver also has a tendency to
break any page which includes a form. The login page
is sblogin/login.shtml and the denied page is
sblogin/badlogin.shtml. While there is no requirement
for you to make any changes to these pages at all,
we do suggest adding a customer service link on
badlogin.shtml so that members know what to do if they
have trouble remembering their user name or password."

hope that helps. i haven't tried it yet as we just got it set up.