We use SSH to do the trick. We haven't had the time to look into NIS yet so we made some small perl-scripts to use with Samba and passwd (our clients are running Windows).
With SSH you can do the following:
SSH your_server '/usr/bin/passwd username'
I know this isn't the most secure way to do it but it's running behind severel firewalls and only sys-admins are allowed on this lan. So it's working for us and might do the trick for you.