I have a Power Mac G4, and I found my old USB 2.0 PCI card. I plugged it into the Mac, and its recognized by the System Profiler, and works with USB 1.1 devices like keyboard and mice, but USB 2.0 devices will not work. Sometimes, it will show the flash drive under "High Speed USB" but will never mount. I am running 10.5.8 if that matters.