Create your own Windows XP logon message
Click Start, click Run, type regedit, and then click OK. In the Registry Editor, drill down to the following key: HKEY_LOCAL_MACHINE\ SOFTWARE\ Microsoft\ Windows NT\CurrentVersion\ Winlogon. Right-click LegalNoticeCaption, click Modify, type My Windows XP Machine, and then click OK. Right-click LegalNoticeText, click Modify, and then type your message. Close the editor and your new message will appear at every log on.