How do I set up a Mac as a NIS client?
I just set the domain name once as root (using sudo) and launchd has launched ypbind for me ever since. The man pages for yp and ypbind might come in handy.

Is /etc/defaultdomain set? You could issue a ypbind -ypset to see if any servers are responding but it's better to have a list of masters and slaves laid out in /private/var/yp/binding/DOMAINNAME.ypservers