It is the Farallon Ethernet PC Card drivers, although I didn't expect these to work as it's not a PC Card.
The most luck I've had was with the 'PB1400 EN Installer 1.6 '. Once installed and restarted, immediately when the Finder loads I get an error message saying "No valid ethernet address was found", and "An error occured while trying to use Alternate Ethernet, Make sure your network connections are correct". I can set the TC/IP control panel to use alternate ethernet ok, and have also tried setting a static IP Address. When I select Alternate Ethernet on AppleTalk I get the error message again and it switches connection back to Modem (default). I'm assuming the 1.6 drivers are meant for System 7?
I've also tried it in another PB1400 and had no luck, the green light on the card is on and everything. On the actual card beside the ethernet port it says "EPIC" which is the codename for the card. I read somewhere that these were different from the standard Farallon cards (I don't know how correct that is since it is a Farallon card), but perhaps it requires different drivers to the original Farallon ones?