http://www.agilent.com/cs/agilent/en-us ... stationrev
Looks like Version B is the latest to support 5971 native, if you upgrade the motherboard to a 5972 then you could probably use Version C.
Version A was supported under Windows 3.11 and Windows 95, Version B and C are supported on Windows NT4.0 up to SP6a with the latest version.
Version B will support the 5890GC but you would need to use a 6890GC if you go to Version C. The SCII (smart card 2) was in the later models, the early models came with the SCI (smart card 1). From the chart the SCII+ came in the last models of the 5970, but I know I was able to take a SCII+ from an old 5970 and use it in a 5971.
There were some tricks to get the 5971 to work on newer software but most involved making it appear to be a 5972 or some editing of ini files but I don't remember what those were. If you are running a 5971/5890 combination you are stuck with needing a Windows95 or WindowsNT 4.0 PC and if lucky you can make it work with a PCI slot GPIB card, but many of the cards that shipped with the instruments were for ISA slots in the control computer. We had to replace our last few 5890s a few years ago simply because our WindowsNT computers were on their last legs.
If it weren't for forced obsolescence Agilent would sell very few new instruments because we would all still be using the old ones