It's been a few years since I've looked at it, but I'm almost sure the field adjustment software has its own built in driver that talks directly to the GPIB card. I don't think you even need the DOS driver installed.
This is correct. Someone around here wrote a QEMU driver for that specific GPIB card, so the TDS FAS could be run in DOS inside QEMU. It essentially forwards commands to the Linux /dev/gpib interface if I remember correctly.
Basically, you can go with that option and a reasonably new GPIB adapter (USB, LAN or PCI based) *or* you can buy the required NI GPIB adapter (ISA based) on eBay and run the software on an old PC.
I'm still not sure why Tek hard coded the drivers into the FAS. There seems to be no reason they couldn't have hooked into NI's own drivers... Hell, NI even provides examples, headers and libraries for several dialects of BASIC, C and Pascal!
If they had used NI's drivers, it would have made it very easy to do what (I assume) you're trying to do; that is, run the software in a VM and use a serial based GPIB interface.
I actually have an old PC (a pimped out Compaq Portable III) with an ISA GPIB card (the ASIC based PnP version) I was planning to use for the FAS, but couldn't because of the stupid hard coded drivers.
That said, most of NI's ISA cards were very similar, so I was thinking of decompiling the FAS and seeing if I could get it to work with my card.