Login users off the server?

Win2k Advanced Server, is there a way to log users off the server from the server??
or at least log them of from an application running on the server? the problem I had was that some users left home with out login out of an application we run on the server, so when I try to back up the data file I can’t because some users still loged in! how can I get arround that??
Thanks!
Marlon D.