Quick question that I just remembered others have run into. How long are your passwords required to be? By default DNN sets the minimum password length to 7 characters. If your passwords are less than this it will not log you in manually. The password length can be changed in your web.config. Do a search for PasswordLength (I think the actual variable is MinPasswordLength but I'm not 100% sure) in your web.config and adjust it to whatever your domain requires.

To turn of automatic logins (stop DNN from redirecting to WindowsSignin.aspx) just comment out all instances of <add name="Authentication".... /> in the <httpModules> section of your web.config.

The Auto-Login IP Address; could you give me an example of what you've put in there? Computers within the IP range should be attempting to automatically log in (though if you comment out the line mentioned in my last paragraph this feature isn't used).

As to your last sentence I'm a little bit confused. Are you wanting your users to have to enter their credentials or do you want them to be automatically logged in when they follow the link to WindowsSignin.aspx?

As I said in my reply to you on my blog, I've got some ideas on why it's taking so long but I need to do some testing to see if my theories are correct and I haven't had the time to dedicate to it. I should be able to in April though.