The Dell machine arrived. After much faffing around trying to get Windows 98SE running on it, I decided to go for a simpler solution.
So, I have downloaded Freedos into a bootable CD, booted the machine with that and created a 2GB (cuz that's how big a normal DOS partition could be) partition.
I then installed Linux on the beast, running dual boot so I could get the machine on the network, and copy over the files from the Fireball server on to the DOS partition. (Linux can write FAT file systems, you know).
I then ran Freedos up, so I could try to run LIFUTIL - and was shocked to find it works. Now all I have had to do is to find a 720K diskette, format it in LIF format, and then put the right driver for the 1GSa/s card on. I went through all the files, and eventually found that the SYSTEM_0.13 file was the correct one, put that on the disk and move it over to the HP 16500A front drive.
Wow. We have a working scope.