unix and userdb password sync

[macky@staktrading.com]

Is there a way of syncing unix passwords with the userdb,

Example:
Create login name for user in mv, then automatically create a unix user.

ie using minivend to change a password in /etc/passwd to the same as the
password in the userdb?
or using a common sql/nis database for both?

I can write an /etc/passwd file with mv and this works fine but very
dangerous( little security,easy to break all logins)

Thanks,

Macky..