Does anyone know of good resources for an audit of Windows and Active Directory security?

I'm engaged in an audit of Windows and Active Directory. I'd like to know what to look for, how to audit the GPO, and the easiest way to audit user permissions.

There are several audit programs available for Active Directory. If you are a registered user of AuditNet there is a free program available after logging in. I also have an AD audit program available by request in exchange for an original audit program not currently in the inventory.

Jim