Change the default application install from C:\Program Files: 

If you want to change the Default application install from "C:\Program Files", use Regedt32 to navigate to:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion
Alter the paths at: ProgramFilesDir
AND
ProgramFilesPath
You may also alter: CommonFilesDir

Changing the default WinNT install path: 

If you want to change where NT expects to find the NT CD, edit:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Sourcepath
and
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup\Sourcepath
If your CD drive is D: and you are working with an Intel-based machine, the value should be D:\I386 and D:\ respectively.

If you want to tell NT to look on your hard drive for the installation files, then
use the path and drive letter where you have copied your I386 files.
e.g. C:\I386 and C:\ respectively

Tell Windows NT 4.0 where to look for a service pack stored on the hard disk 

If you install the service pack from a hard disk location, NT 4 will remember and look there when it needs a file. If you didn't install the SP from its current location, you can use RegEdit to tell Windows where to find it.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup
In the right pane, double-click ServicePackSourcePath and set the string to your new path. Choose Registry, Exit to close RegEdit and then restart the computer.

Remove unwanted items from Add/Remove programs:  

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall
Delete any program names you no longer need.
Note: Use the same registry key in Windows NT, Win9x, Win2000

Opening My Computer icon on the desktop in Explorer View: 

If you hold down the Shift key while you double-click My Computer, it will open in the Explorer view. To make this a permanent change, you can edit the Registry. Keep in mind that the Registry change will cause all folders to open in the Explorer view.

HKEY_LOCAL_MACHINE\Software\Classes\Folder\Shell\Open.
Click the arrow at the left side of the Open folder to expand it. Next, click Command to select the folder.  Double- click the (Default) value in the right pane and change the value to:
%SystemRoot%\Explorer.exe /idlist,%I,%L
Next, navigate to:
HKEY_LOCAL_MACHINE\Software\Classes\Folder\Shell\Open\ddeexec.
Double click (Default) in the right pane and replace the current value with:
[ExploreFolder("%l", %I, %S)]

Turning off 8.3 file name generation:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem

Change the NtfsDisable8dot3NameCreation value to 1
To clear the pagefile at shutdown, add the REG_DWORD value:  
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\ClearPageFileAtShutdown and set it to 1

Enable Shutdown button on the Logon Screen   

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon. In the right pane, look for the value named ShutdownWithoutLogon.
To change the value, double-click it. You’ll then see the String Editor. Enter a value of 1 in the String field and click OK.

If the value doesn't exist, you'll need to add it. Select Add Value from the Edit menu. When the Add Value menu appears, enter the name of the value in the Value Name field exactly as listed above. Make sure the Data Type list box contains the value REG_SZ and then click OK. You'll then see the String Editor screen. In the String field, enter a value of 1

Displaying Your Company Logo (or other bitmap) during logon.
Design an appropriate bitmap and place it in your NT directory as YourLogoName.BMP. Use 8.3 naming convention.
Edit: HKEY_USERS \.DEFAULT\Control Panel\Desktop
Double click or Add Value REG_SZ of Wallpaper and set it to the full path to YourLogoName.BMP.
Double click or Add Value REG_SZ of TileWallpaper. 0 is Don't tile, 1 is tile.
Double click or Add Value REG_SZ of WallpaperStyle. 0 is normal, 2 is stretch to fill the screen (which is mutually exclusive with TileWallpaper = 1).
If you use a normal, not tiled logo, you can position it by adding the following REG_SZ values:
WallpaperOriginX set to the number of pixels from the left hand edge of the screen.
WallpaperOriginY set to the number of pixels from the top of the screen

Managing the Mapped Network Drive dropdown list.
If you want to remove some the connections in the list, edit:
HKEY_CURRENT_USER\Software\Microsoft\WindowsNT\
CurrentVersion\Network\PersistentConnections
Highlight and delete unwanted entries. Then double click Order and remove the letters that have been deleted. You may rearrange the letters to change the display order

Hiding a server from the browser.
To hide a server from the browser, edit:
HKEY_LOCAL_MACHINE\\SYSTEM\CurrentControlSet\
Services\LanmanServer\Parameters
Add value Hidden (REG_DWORD). Set it to 1.
Reboot the server. It may take up to ‡ hour for the server to disappear from the browse lists