The first entry (USERINIT) is responsible for executing the shell program.
To start your program before the shell, you may replace this entry with
your own program. If you do so, your application is responsible for
launching the shell (Explorer.exe in Windows NT 4.0).
Explorer.exe is the standard shell in Windows NT 4.0. It can operate in
two modes:
Browser mode (similar to File Manager)
Shell mode (to manage the desktop, taskbar, and Start button)
When you launch Explorer.exe, the following conditions are checked by
Explorer.exe to work in shell mode:
No instances of Explorer.exe are running
It is the standard shell for the system (see shell registry value under
WinLogon key)
If you launch Explorer.exe from your own "userinit" initialization
program, be sure that the shell value always references Explorer.exe,
otherwise Explorer.exe will operate in browser mode instead of shell
mode.