Legal Notice Dialog Box Before Logon

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.