Add An AUP(Acceptable Use Policy) To Your Windows Machine

If you are on a domain you can simply do this with group policy. If you are doing it on a machine you just log into locally you use the local group policy editor:

Start => Run => gpedit.msc
Computer Config => Windows Settings => Security Settings => Local Settings => Security Options

Interactive logon: Message text for users attempting to log on
Interactive logon: Message title for users attempting to log on