In tip 0958, I explained the NoLogoff registry entry for Windows NT 4.0.
In Windows 2000, setting NoLogoff to 1 prevents a user from logging off by any means, including running a logoff program. This setting also removes all logoff menu items and buttons. The entry is used by the Disable Logoff Group Policy at User Configuration\Administrative Templates\System\Logon/Logoff.
To just remove Log Off <UserName> from the start menu, and prevent the user from restoring it, use Regedt32 to navigate to:
On the Edit menu, Add Value name StartMenuLogOff, as a REG_DWORD data type. A data value of 0, the default, disables the policy. A data value of 1 enables it. This entry is used by the Disable Logoff on the Start Menu Group Policy at User Configuration\AdministrativeTemplates\Start Menu & Taskbar.
The reverse of StartMenuLogOff is ForceStartMenuLogOff. A data value of 1 adds the Log Off <UserName> to the start menu, and prevents the user from removing it via Start / Settings / Taskbar & Start Menu / Advanced. This entry is used by the Add Logoff to the Start Menu policy.
NOTE: If you subsequently toggle these policies from Not configured, the registry entry will be deleted, unless the policy is set toEnabled. If you then toggle the policy to anything else, the registry entry will be deleted. This is true for most policy entries.