Not exactly sure what you are asking here ...
Can you maybe explain what you are trying to do.

DNN is built around ms sql and as such all elements of the system require access to that database.

Westa

This is very achievable ... to do so what you would need to do is create your own membership provider. A membership provider is a module that sits inside dnn and handles login access to your site. By default, 2 providers area shipped with DNN the standard login and an active directory based login. You would create a 3rd provider that is dynamically added to the login / logout modules and handles the login process ... internally what this module can do is access your external database and manage the validation process. Westa