I did not install or configure SharePoint on this box but it is in a domain. After creating a web application and site collection, I can not add domain users to the site collection. The OS is AD aware, and I tested this by creating a local group and adding a domain user into that group.
How can I ensure that SharePoint is aware of the domain?
Windows Server 2008/MOSS 2007
In Central Administration, you need to go into the Application Management. Once there, look for Authentication Providers, under Application Security. You should have a Default zone, open that and you will be able to pick your authentication type.
I think I figured out the solution to my own problem. The SharePoint site collection was running in an application pool with local credentials instead of domain credentials.