Map IIS 7.5 Virtual Directory to Microsoft File Server Directory

We are trying to connect an IIS 7.5 Virtual Directory to a Microsoft File Server Directory (via a UNC path) so that we can use a URL to access the directory. The issue we are having is, what type of rights would be needed to allow this. We would like the web users to only have read access to the folder. I would assume we would need to give the IIS_User rights to the Microsoft File Server Directory. In addition, I noticed that there is a Windows Authentication feature under the IIS 7.5 Virtual Directory Authentication that might be the way to go.

Thanks

-Windows 2008 R2 Server