I tried the other drivers here at Driverguide.com and found that they are flawed just like the ones I tried from 3Com's website.
I had downloaded these driver files a while back and they do not give me any problems. All the necessary install files are here including UN3C556.exe among others. Files in this zip are called fem56bx1.exe and fem56bx2.exe. I have only tried these in Win98SE but I would imagine they would work with Win95 SR1 and higher.
These drivers work only with NON-GLOBAL adaptors (LAN + 56K). I have not figured out how to get GLOBAL adaptors working yet.
Hope this helps!