USING ROLES WITH WINDOWS AUTHENTICATION

I'm new to ASP.net and I'm developing an Intranet Site.  I wanted  to use Windows Authentication but I'm not finding a lot of information about using it.  I have set up some roles using the ASPnet Web Administration Tool.  But it looks like if I use Windows Authentication, I cannot enter users, and in fact any Windows user is a potential user.  Is there a way to enter users, e.g. using the aspnet.mdf and entering users directly using their WIndows Login Information?
I have set up roles for my Intranet Site that do not relate to WIndows Roles.  I've been reading ASP.NET 3.5 (Walther) and he wrote that WIndows Authentication uses WIndows Roles.  I'm assuming this is like Administrator, User, Guest.  Do I understand this correctly?  I need much more granularity than that (e.g. Developers, Administrators, Dept1 Users, Dept 2 Users).  Is there any way to do this using Windows Authentication, or do I need t ...