How do you set Role-Based authorization for Windows Authentication?

[Bob Osborne]

I am working on a company ASP.NET Intranet web application.
I am using IBuySpy protal as my "go-by". It uses Forms
authentication.
I changed it to Windows authentication, but I cannot
determine how to set the roles for myself.
It is using the public function IsInRole a member of
System.Security.Principal.IPrincipal
My application is on my computer (Windows 2000).
If I use Forms Authentication, I can make changes to the
application, but in Windows authentication I cannot.

How do I set my role to MyAppAdmin or something so I can
give myself privilege to edit the application?