Mixing Forms authentication with Windows authentication
Solution 1:
Actually, you can do it. Bit late for @dr_draik, but this cropped up in a google result for me so I thought I'd share some knowledge.
If you're in classic mode - Enable both Windows and Forms auth. You'll get a warning about not being able to do both at once, but you can ignore it. Then, you can spelunk around various properties like Code:
HttpContext.Current.Request.ServerVariables["LOGON_USER"]
and fish the username out of there.
If you're in integrated mode - 4021905 IIS7 Challenge-based and login redirect-based authentication cannot be used simultaneiously leads to IIS 7.0 Two-Level Authentication with Forms Authentication and Windows Authentication which is a module that allows you to selectively change the auth for different pages.
Solution 2:
You could always set up 2 separate application in IIS7. One would have Windows Authentication enabled. The other would be the main app with forms authentication. If a user went to the windows authentication app, the page could grab their credentials and pass it to the forms authentication app.