Open the Registry Editor.
In Windows 9x and Me, navigate the left pane down to
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Winlogon.
In Windows 2000 and XP, go to
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon.
If you don't see an icon labeled LegalNoticeCaption, right-click anywhere in the pane, choose New, String Value, type LegalNoticeCaption, and press
Enter. Create a String Value icon named LegalNoticeText, if it doesn't already exist in the Winlogon key.
Double-click LegalNoticeCaption. In the 'Value data' box, type the text you want to appear in the message's title bar (you can leave this blank if you prefer),
and press Enter. Next, double-click LegalNoticeText, type your message in the 'Value data' box, and press Enter. The warning dialog box accommodates
a pretty large paragraph; if you plan to input more than a couple of sentences, you should probably compose the message in Notepad or another text
editor, double-check it, and then paste it into the 'Value data' box in the Edit String dialog box. To remove the message later, simply return to this setting
and delete any text you added for LegalNoticeCaption, LegalNoticeText, or both.