Win2000 passwords

I have done a number of Win2000 installations. The passwords are needing to be changed. When the users change their passwords they can no longer go in with their new password - I have to go in as administrator, change their password and then they are ok. I want them to be able to change their password without problems under the group Standard - Power User. Better yet - I would like the password not being requested to be changed until I as administrator of the network want them changed & then I will do it. Can anyone help me?