Corporations have been using this functionality for years. You can have your copy of Windows display a message on the screen before logon. Typically, these messages are legal disclaimers, things like this:
This utility will let you set the logon text. There are two fields, Title and Body. The Title is the larger text at the top. The body will be the main message in-between the two divider lines and making up the center of the screen. The user will have to click OK to proceed to logon.