How can I configure default settings for new users?

Start the registry editor (regedt32.exe)

Select the "HKEY_USERS on Local Machine" window

Select "Load Hive" from the Registry menu

Move to %systemroot%ProfilesDefault User (e.g. d:winntProfilesDefault User)

Select Ntuser.dat and click Open

When it asks for a key name enter anything, e.g. defuser

Now select the username (e.g. defuser) in the "HKEY_USERS on Local Machine" window and make the changes (for example you could change the wallpaper by changing defuserControl PanelDesktopWallpaper )
Note - If you add new keys make sure everyone has at least read access otherwise it will not be copied

When you have made the changes select "Unload Hive" from the Registry menu

Close the registry editor

Logon as an Administrator

Start the System Control Panel Applet (Start - Settings - Control Panel - System)

Click the User Profiles tab

You will see a list of all the profiles stored on the machine. Select the one which has the settings you wish to use as the default for the domain

Click the "Copy to" button

In the "Copy profile to" enter the location of the Netlogon share of the PDC (usually %systemroot%system32ReplExportScripts, you want the Export area not Import as anything in Export is copied to the import by the replication process), e.g. h:winntsystem32replexportscripts (if h was mapped to the c$ drive of the PDC).
In the "Permitted to use" click Change. Select Everyone and click Add, then click OK.

Click OK to start the copy.

You should then check that the file ntuser.dat has been created where you selected.