> In short, even after following the above suggested
> method, I'm having no luck backing up a secured
> Google Sites, site.  It's unclear where I specify
> the username/password.

1) A mirror is not a copy, not a backup. It is a static snapshot in time.
Forms will not work. You can NOT get server side code.
2) You go to the login form and follow the capture procedure. You enter the
username/password in the form. Don't forget to filter out the log-out url if
any.
3) HTT will not capture httpS urls.
4) Always post the command line used (or log file line two)