From your description, you would use the ID column as the Username.
the concept behind security assist is to login using a Username and password, once logged in, the ID of the user is stored as a session.
From your explanation, you would set the ID column to be both the ID and the Username.
This is not a standard use of security assist though, it is not usually used with the ID as a login value. you will need to go to the mage pages tab, and edit the field settings, and change the ID column form a text only field to a text field.
you say the pages that are being created don't display in the browser, do you mean they are just blank pages?
a blank page means that a php error is occurring but error reporting is turned off.
to turn error reporting on, add the following code at line 1:
once we know what the error is, we will be able to troubleshoot the cause.