I'll keep the advice re: Panther in mind.

So, I finally got Tiger installed and Ethernet works fine. I don't get it, but I'm also not going to argue with it.

Installing Tiger was bad enough... the ancient DVD drive didn't like my DVD+R copy of Tiger and only tolerated a DVD-R copy until near the end. I finally had to use a USB DVD drive (at 1.1 speeds).

Stilll not sure what I'm going to do with it, but at least I feel like it works.