Not to destroy the use of Kixtart for everything, but why not display this with group policy? When a user hits ctl-alt-del it pops up a window before giving the user a chance to logon.

Computer Config >> Windows Settings >> Security Settings >> Local Policies >> Security Options >> Interactive Logon: Message text for users attempting to log on

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Computer Config >> Windows Settings >> Security Settings >> Local Policies >> Security Options >> Interactive Logon: Message title for users attempting to log on