In case anyone struggles in figuring out what to do with this card, here’s the deal. On eBay, there are cards labeled as IBM 100/10 Ethernet Adapter, which is a fairly odd, as 100mbit ISA cards aren’t too common. They look like this:
These cards tend to come with part numbers like 25H3511 or maybe 25H3501. I’ve also seen them referred to as IBMFEI cards in some literature. I found a resource online with the mapping of these cards to drivers, which can be found here. Ultimately, for DOS, Win 3.1, Win95, or OS/2 you’ll want to get a hold of ETI1001.EXE (and optionally ETI1002.EXE if you’re using SCO). These are DOS executables which end up writing a floppy image to a 1.44MB diskette, so have one ready.