Included in the NI software you installed (which i assume was NI VISA and maybe some other things) should be a program called NI MAX - measurement and automation explorer.? I suggest using that to determine if your computer sees the instrument or not.? Once the program opens, in the tree on the left, expand devices and interfaces, and you should see the usb-gpib and connected instrument (and if not, you know what your problem is). ?I'll be away from my 8510c for a few days but if you're still working on this by the time i get back to it i can send some screenshots.
If the adapter shows up but the instrument still doesn't, i suggest checking that you're connected to the correct gpib port on the 85101c (display unit) - one connects to the other boxes in the stack, the other to the computer.
I believe that the driver you reference would be useful only if you are using labview, so i don't think it's what you are looking for.
I also recommend downloading the ke5fx toolbox, I find the VNA tool to provide a huge quality of life improvement when using my 8510C.
