How to Create a Windows Auth Logon Page

I have an ASP.NET intranet application using Windows Auth. Internally, it works, but it uses the browser popup to prompt for credentials. I would rather have a logon page handle this. I have searched but haven't found demo code for a logon page that will pass Windows credentials, let alone a descriptive tutorial. My other issue with the current setup is that when a user is connected VPN, and using Internet Explorer, Windows prompts the user to authenticate to the web server (looks similar to an RDP session), but authentication here doesn't work. Firefox bypasses this check and lets the user enter their Windows credentials in the Firefox logon popup. Any insight into either of these? I'm using ASP.NET 4.0, Windows Server 2003, IIS 6.0.