the security assist wizard is used for creating the security assist pages for you.
if you want to use pages wand forms that have already been created, you will need to apply the security assist behaviors to the pages manually.
the registration page is just a page that displays a form, and stores the entered information into a database table using an insert record behavior.
if you want to use your own pages, you will need to add the insert behavior to the registration page, then create the login page and add the log in form and the authenticate user behavior.
it is much easier to use the wizard to create the pages, you can apply your site design to the pages that are created after the wizard is done.