Questions On A Mixed-mode Authentication

First post, so greetings!

I've been using ASP.NET 2 authentication from an MS SQL 2k5 database now in the web application for my company's customer accounts (file serving, custom webreports, etc).  There is currently no support for employees through this web app, but in our plan to go paperless it's become of interest to let the employees access much of their information through the same web portal.  The catch is, I'd rather not make them have to use two accounts (one for their domain authentication and one for their web authentication).  It's already taken a lot of conditioning to get them to memorize a single username and password.

So what I really need is the single Login.aspx page to accept both ASP.NET logins and Domain digest logins, and the Domain digest login needs to be HTTP based (not named pipes).  Is this possible at all, and if so, is it possible without making an isapi filter?  After all, Microsoft Office Outlook Web Access is served by the exchange server and accepts active directory passwords.  So how could I do authentication in this way, and if so, is it possible to have the Outlook Web Access form be accessible from the same session as that of my web server?
 Thanks, I surely hope someone can help. . .
 -Brandon