I have an old FreeBSD book but not a NetBSD book. I do not know how similar they are. In the FreeBSD book it says the adduser command can be used to add a user and the passwd command can be used to add or chage a password.
This is a Linux users forum, so most of us are not experts on versions of Unix such as NetBSD. I doubt that NetBSD would do a better job of recognizing your modem that the latest versions of Red Hat, SuSE or Mandrake Linux. Is there any chance you will exentually just get a different modem? An external serial modem is usually much easier to install under Linux (but not many of the external USB modems). An internal modem that has says it has a built in UART chip and says that it is compatible with Linux would also be very easy to install. Do you have a desktop computer or a tower? I have never really tried to install use a winmodem under Linux so I do not really know how easy or difficult it is. After reading many of your posts over the last few weeks, it looks difficult. Below is a link to a webpage that talks about winmodems and other types of modems. The web page is over a year old but is still interesting.