ADB to USB adapters

I'd like to connect an old ADB keyboard to my G5 iMac running OSX 10.4. I've found the Griffin Technology iMate, but its info says that it only works up to OSX 10.3.9.

Does anyone know if this is truly so? Might it possibly only apply to more complicated things like WACOM tablets and dongles? I just want to hook up a simple keyboard.

If it's truly so, does anyone have other suggestions on what I could try? I've found other adapters (usb-port.com, Dr. Bott) but they don't say anything about operating system incompatibilities.