Legal Notice Dialog Box Before Logon

To  Legal Notice Dialog Box Before Logon follow this step:

Start/Run/Regedit

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon

Modify the value named 'LegalNoticeCaption' to represent the caption on the dialog box (e.g. 'WARNING!'). If this value doesn't already exist create it. Modify the value named 'LegalNoticeText' to represent the body of the dialog box (e.g. 'Do Not Attempt to Logon to this system unless you are an authorized user!') 

Exit your registry and restart Windows, and the next time you boot up you should be presented with the dialog box before logging on.