Force user to log off

I Administer a small network that consists of three Win 2k servers and a mix of Windows 2000, 95 and 98 and a couple of XP. What I want to do is to make sure specific users (all but Admins)to be logged off. I have set the Logon hours to match the time I want them off but what I want is for then to get logged off to the login screen. Now there does not appear to be any thing happening with the users.