PowerPup is thinking along the right lines. PowerBooks based on PCI architecture must use a PCI to PCMCIA or CardBus bridge chipset. Therefore a driver for that chipset is part of the OS. So what bridges were used on PCI PowerBooks? Apologies for asking in the wrong forum.

PowerPup: My bet (without booting my PowerBook 5xx with the card reader that sometimes works with WiFi cards) is that the extension you mention extends the ability of NuBus architecture PBs.