Well, if you can find a working piece of software that does HICAS diags, then you'll be in business. I know Conzult 300zx version has HICAS diags that works on skylines with the OBD1 connector but it costs around $500. I have a consult cable from PLMS myself and some of the free software is nice but not as in depth as one would have hoped. I also have a hexterm program which allows me to send commands to the ECU/HICAS/Auto Trans/Aircon systems but unfortunately the registers I have as a reference don't match up.
I for one would like my HICAS fixed properly, so if you can get a tool to scan codes, I'll be your first customer ;P
-D