AT-FBUS can work under Windows 2000 in NI-FBUS 2.3.5 or later version. You don't need to install the driver, the AT-FBUS driver "nifb.sys" will be installed to your system driver directory automatically.
AT-FBUS doens't support PnP feature of Windows 2000, so you need to start the driver from "non-Plug & Play" list instead of importing the "INF" file as PCMCIA-FBUS does.
You can refer to the attached "FF HW and NI-FBUS SW for Win2000/XP" Installation Guide document for details.