Windows NT does not cache passwords. If a VisionFS server is using UNIX (unencrypted) passwords for authentication, or another VisionFS server that's using UNIX passwords, then users will always have to type a password to access the VisionFS server.
To allow users to access a VisionFS server from Windows NT without typing a password, the VisionFS server must use one of the other authentication methods. In addition, a user's Windows password must be the same as the user's password for accessing this VisionFS server.
If you switch to using UNIX passwords from another authentication method, users must log out of Windows NT and log in again, otherwise Windows NT won't allow them to connect to the server.