To remove the shutdown button from the logon screen in WinXP and 2000,
1) Just goto->
START-> RUN-> type Regedit
2) Use regedit and navigate to the following key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system change the value of the dword 'shutdownwithoutlogon' to '0'.
And then exit regedit.