Looks like its a Wireless-G Compact Flash card in a PC Card adapter. There are a few CF Wireless-G adapters out there that are MUCH cheaper, but have the antenna plastic stub. The other problem is lack of Macintosh drivers. These CF devices have Windows CE and XP drivers from what I can see.

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Hence the reason to find out what chipset they have. There are numerous third-party WiFi drivers for OS X out there - and chipsets that are used in the AirPort and AirPort Extreme cards are natively supported. (There is a CardBus card you can throw in a PowerBook G3 (Wallstreet or above,) or Titanium PowerBook G4 that is recognized by OS X as a native AirPort Extreme card.)