I have the adaptor, and Win XP. It works great. Here is the instructions from my floppy install disk:
USB Controller Drivers 11-03-2002
Hardware:
GameCube Adapter
Operating Systems:
Win98, WinME, Win2K, WinXP
IMPORTANT: Install software before plugging joystick adapter in.
To install software:
Double click "setup.exe"
If any previous drivers have been installed, a dialog will be shown,
listing those drivers that have been removed.
Windows will then copy the necessary files, and may ask you for
your Windows CD, and the current install directory.
Once the software is installed, the adapter can be plugged into the
USB port - after a short delay, an entry will appear in the Control
Panel for Game Controllers.
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