Though it took typing a nasty NVRAM patch into nvedit by hand, I finally got the unbootable G3 to boot NetBSD off of its hard drive. If I'd been able to boot into MacOS, it would have been a few clicks. But I do have a nice collection of Open Firmware links and a deeper understanding of those whacky Macs now... Open Firmware is pretty interesting, really. sigh Too much too learn.
Tried X real quick, and it's working at least. I never did get X to work right on my NetBSD/i386 box at work. I guess I'll have to get pkgsrc onto CD and install some goodies.