How would you import user names and passwords from a UNIX database to windows server 2003?

You can export the user names easily from a Unix password file - it is stored in the /etc/passwd file. The passwords are a different matter because they are hashed and cannot be imported into any other system to be useable.

After you export the user names from the passwd file, use the 'dsadd' command of server 2003 to import them. You can give them a random password or a default password with the dsadd command.

If you are speaking about exporting from a true database, then that would be dependent on what database you are asking about.