My only experience with a USB2 card upgrade was in a PM G4. The only one that could be picked up off-the-shelf was a generic PC one with a Via chip. Turned out to be useless. It was for a USB2 external drive that was to be used for backups. Trouble was, the drive would only mount maybe one out of every 10 times. It worked fine with the built-in USB ports. Even the Via drivers didn't help. But this was with Tiger too.