We have an Ultra2 box that is hooked up to a serial console that screws up the format when trying to edit files. It is much easier to use an xterm session over the network, rather than rely on the configuration of our serial console/terminal. Anyway, since we were trying to edit files that set up the networking, we have a wee bit of a catch-22. The command line to set up the networking is:

ifconfig hme0 inet 10.50.100.49 netmask 255.255.255.0 broadcast + up

Of course, your interface may be something different, but just replace hme0 with the interface name.