Thanks to the Free NIC drivers for Solaris page, I got the vfe driver working for the VIA Rhine III onboard Ethernet. I followed the instructions, and tried loading the precompiled drivers first. No go. I recompiled them and it worked.
I found out that Solaris 10 now ships with gcc and gmake, as well as other Sun Freeware, in /usr/sfw.
I enabled DNS by replacing /etc/nsswitch.conf with /etc/nsswitch.dns. I selected “no naming system” on installation.
I was able to register the system using my Sun login. It’s now downloading the free security updates.