However, now I need to use it from a Windows 8.1 / x64 machine, from the Arduino IDE, and I can't get it recognized.
I downloaded and ran the zadig.exe installer (from an administrator command line window.) When I plugged in the USBtinyISP, it detected the VID/PID, and I selected "install driver."
It seems to install fine, and Windows disconnects and then reconnects the device. However, when I choose "Upload using Programmer" in the Arduino IDE, I still get the error that it can't find the USBtinyISP:
avrdude: Error: Could not find USBtiny device (0x1781/0xc9f)
I'm sure this is some bullsh!t Windows USB driver signing blech going on -- but zadig is supposed to work for Windows 8, right?
How can I make this product actually work with my computer?