I'm using the GPIB adresses 15 and 20 from the software config from the old PC.
I made a HPIB test on my old system, I found the GC and MSD on GPIB 715 and 720. Their GPIB adress is also 15 and 20, so I think the 7 ist the "logical unit" from the IO libs settings.
In the VISA settings I can identify the MSD on GPIB 20, the GC only generates a timeout.
The only thing I found about this software and WinXP is, that it is not sure if it will work. But the software seems to work so I hope I can get rid of the connection problems.
If I remember correctly the default GPIB address for the card in the computer is 7, but you may want to check that to make sure your card is set correctly. If it is set to a different number then things won't talk to each other.
I did have a card once that went bad and would talk to the MS but not the GC, and when I put it in a computer for an HPLC it would talk to that also, just not a GC. It was strange as it should either work with everything or nothing.
You can trouble shoot the cables by disconnecting the MS and using different cables to connect the computer to the GC, it could be one cable has gone bad. I normally hooked them up computer to MS, then piggyback off the MS to the GC, then the GC to the Autosampler if one was attached. Those cables can go bad so be sure to check them to make sure they are good.