In Previous versions of Windows NT, CTRL+ESC would bring up a Task List.
In Windows NT 4.0, CTRL+SHIFT+ESC starts the Task Manager.
CTRL+ESC raises the Taskbar and the menu. Then, to invoke the Task Manager (Taskmgr.exe), right click on an empty area of the Taskbar and choose Task Manager.
If you wish CTRL+ESC to display the Task List (I don't know why, but I have had many requests), edit:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\Current Version\Winlogon
and add Value Taskman of type REG_SZ with Taskman.exe as the string.
You could use this entry to install your own Task Manager in the shell. You will need to reboot.