Windows NT 4.0 asks the following questions before creating a new profile:

Is there a roaming profile defined in User Manager for Domains and does it exist? If yes, use it.
Does this user have a local profile? If yes, use it.
Does Default User exist on the Netlogon share of the validating Domain Controller? If yes, use it.
Does Default User exist in %SystemRoot%\Profiles?, if yes, use it. If no, I don't every want to find out.

To create a new default profile for your domain:

Log on to a workstation as a new generic user (one that does not have Administrator rights in the domain).
Set up the desktop and change any settings. Log off the workstation. The profile is actually created at this point.
Log back onto the workstation as someone who has Administrator rights to the local computer and in the domain.
In the Control Panel / System /User Profiles, select the user's profile that you created in the previous step and click Copy To.
Permit the group Everyone to be able to use the profile.
Specify the server name and the share name, as well as the name of the profile that you want to copy this profile to in \\Servername\Sharename\Profilename format.
NOTE: The name of the profile will actually be a directory name. The entire directory and its subdirectories and files are the profile.
Copy this profile to the Netlogon share and rename it to Default User. This will enable Windows NT to create a new profile based on this profile for a user who does not already have a central or local profile. You should also copy it to %SystemRoot%\Profiles on this server for the sake of consistency.
NOTE: This Default User profile will be used to create new Roaming Profiles as well as new local profiles.

If you apply any of the registry hacks mentioned for HKEY_CURRENT_USER to these profiles, they will be applied to all new users. Don't forget to replicate this to all domain controllers.