To remove the Log Off [Username] command from the Start menu, use Registry Editor to modify the following key.
Open your registry and find the key below.
Create a new binary value, or modify the existing value, named ‘NoLogOff’. Modify the value to equal ’01 00 00 00′ to disable the Log Off prompt, or ’00 00 00 00′ to enable.
Note: You may need to restart Windows for the change to take affect.
Note: This setting relies in Internet Explorer 4.0 or greater being installed.
Key: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
Value Name: NoLogOff
Data Type: REG_BINARY
Data: 01 00 00 00
More Info: http://support.microsoft.com/support/kb/articles/q177/9/03.asp