Multiple authentication/membership providers?

I am developing a webapp that will be accessed by internal users (who have AD accounts) and also external users (who don't have AD accounts).

Can I setup ASP.NET membership stuff to allow the internal users to authenticate with their AD login details, have the external users authenticate against a SqlMembershipProvider, and have both sets of users use the same store for profiles/roles?
I wanted to be able to link all users to information in other DB tables, but i'm not sure if that would be possible using an AD auth provider. If it's not possible, then I'm guessing I would have to store all users in the SqlMembershipProvider?

The only reason I thought about using AD auth was to prevent internal users from having to remember two sets of account login details (AD and webapp).