There are a few options I can think of.

To answer your questions:
1. Yes, you can set which page is the default login page for the site. You can change the default login from /login.aspx to something else. You can set this in admin > site settings > advanced settings. You create a page called like "userlogin.aspx", put your custom module on it, then set it as the default login page.

2. Ultimately you will have to authenticate to the DNN framework. If your module first checks authentication against LiveID, OpenID, etc, it will then have to log that person into the DNN framework. This can all be done programmatically, no problem. Just have your module take the user credentials, authenticate to LiveID, then check DNN database for that user. If the user exists in DNN also, login to the DNN framework. If it doesn't, create it and login. First you handle the authentication to the external source, then with same credentials authenticate to dnn. It can all be done behind the scenes easily. It's kind of a hassle but the bottom line seems to be that in the end you will have to authenticate to the DNN framework regardless of what you did before that.

Hi Kelly,

Thanks alot for the reply.  It sounds like a custom login module is the way to go, rather than a custom Authentication Provider.  And so to be clear, I can intercept logins.. validate against external data source - then look them up in DNN - if they aren't a user, add them and login them in, otherwise just login them in.

Thanks for clarification!

Jay