Remote User Authentication in Windows 20

I have a user in another state who is using Windows 2000 Professional and is still able to connect but I have a worry that he is using a cached account or something. When he tried to log on to the local machine as administrator, it gives an error that he can not log on interactively with those credentials. I don’t really knwo how to proceed or really no where to start to fix this problem. Any help is already appreciated.

tech_nt@yahoo.com