I just set up a little server for a friend and shared the D: drive and the related User directory. When I log on, the default user directory mapping doesn't appear and when I try to manually map the drive it prompts me for a password.
1) Did you actually install Active Directory after the OS install?
2) Did you join the other computer to the domain?
3) Did you create the Domain User account?
4) Did you log into the other computer with a Domain account?
When you logon to a workstation on a domain, you can either logon to the local account created when the workstation was built or you can logon to the domain account you created on the Domain controller. When the logon box appears the third field should say: