mixing windows authentication and sql role store

hi,
 i'm writing an intranet website, i enabled windows authentication so every user accessing the website will be authenticated.

 For the roles setup i need to use an sql db, i wrote custom roleprovider for it, but i have no idea how to mix those two.

parts of my current web.config:
1 <location path="User.aspx">
2 <system.web>
3 <authorization>
4 <allow roles="Access" />
5 <deny users="*" />
6 ...