Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Control\Lsa
Name:
RestrictAnonymous
Type: REG_DWORD
Value: 1
To see the level of informational exposure NT has as default, download winfo and run it against your PDC. Also check my page on Penetration Testing, Hacking and Intrusion Detection.
Related:
Q143474 - Restricting Information Available to Anonymous Logon
Users
Q184018 - NDS for NT does not support restrict anonymous
connections
Q168464 - Directory Replication Fails with Event ID 3216