Windows Authentication with ASP.NET MVC

I’ve built a custom login system for my asp.net mvc 1.0 web application as I store large amounts of user data for each user (I decided against trying to add custom tables for the windows authentication due to this). The login system basically uses SQL Server (2005 or 2008) and my own database and table structure which is pretty standard. A users table with an unique id, username and hashed password which is linked to my other tables of user related data.