After treating myself to a new Yaesu FT 817 HF, 6m, 2m & 70cm transceiver, I also ordered a CAT to USB control cable from Radioarena (Yaesu USB Programming / CAT Cable for FT-100 / 817 / 857 / 897) which arrived 8 days later.
After struggling to get the recommended drivers to install on my Windows 8 computer I found that the Prolific USB to Serial Com Port chip used in the cable PL-2303HXA doesn't have any Windows 8 drivers and would not run reliably with the Windows 7 driver on an X64 install of Windows 8 with frequent lockups and crashes.
I had previously had serial communication issues with the Prolific USB to Serial Com Port under Windows 8 on a friend's computer who was using the USB converter to talk to a cutter and the only way to resolve it was to buy a better quality FTDI-based USB to Serial converter which worked out of the box on X64 versions of Windows 8 and also Windows 7.
I’ve now ordered an FTDI USB Cat cable from eBay so hopefully, this one will be delivered quicker and work to allow me to control the radio via the PC.
In future, I will be checking with cable suppliers to see which chip their USB to serial leads are using and avoid anything using the Prolific chips!
Update: The new FTDI-based lead arrived and works without any problems on Windows 7 and 8 x64 versions and the radio is now talking to HRD 5.