I'm sure this is a dumb question, but has there *ever been* a third-party wireless card with an OS 9 driver? (Other than the Lucent Wavelan, which is basically cheating given it's the same chipset as the Apple one and the original Airport was essentially a licensed version of it. Pretty sure that includes the software driver as well. I know there were some companies that were selling other-branded Orinoco-chipset cards but likewise they "just worked" with the existing software.)*
OS 9 was never exactly a hotbed of open-source development so unless someone volunteers to give you the sourcecode for a network card driver they wrote at some point you're probably looking at developing a driver completely from scratch. I'm reasonably sure that the "Airport" support from Apple is pretty much a self-contained bundle and not really a modular framework for supporting arbitrary network cards. Not to say that if you could get the source for it you couldn't cut down on the amount of work required by hybridizing it with parts of a card driver lifted from Linux or one of the *BSDs, but, yeah, source, where is it? (Also, practically speaking, an 802.11g driver absent WPA support is probably of negligible usefulness, so also figure on grafting a WPA supplicant into your hybridized support package.)
I will mention that there *were* a very few 802.11b Mini-PCI cards made that incorporated a variation of the Orinoco/Prism chipset behind what was essentially a minimal PCI->ISA bridge, but I'm extremely skeptical that the standard Airport software would be able to find said chip in the nonstandard place and work with it even if one of those cards were to physically (and electrically) fit in the standard Airport slot. (When these monsters came out the Linux driver for them needed some TLC in order to initialize them properly.)
(* EDIT: Okay, I guess according to a page on LEM there was a Classic OS driver for early Cisco Aironet cards, and there was also a 9.2 driver for a USB device made by Belkin and sold under a few different names.
http://lowendmac.com/2009/wifi-for-desktop-macs-running-mac-os-9/
So Lucent isn't the *only* one. Just close.)
OS 9 was never exactly a hotbed of open-source development so unless someone volunteers to give you the sourcecode for a network card driver they wrote at some point you're probably looking at developing a driver completely from scratch. I'm reasonably sure that the "Airport" support from Apple is pretty much a self-contained bundle and not really a modular framework for supporting arbitrary network cards. Not to say that if you could get the source for it you couldn't cut down on the amount of work required by hybridizing it with parts of a card driver lifted from Linux or one of the *BSDs, but, yeah, source, where is it? (Also, practically speaking, an 802.11g driver absent WPA support is probably of negligible usefulness, so also figure on grafting a WPA supplicant into your hybridized support package.)
I will mention that there *were* a very few 802.11b Mini-PCI cards made that incorporated a variation of the Orinoco/Prism chipset behind what was essentially a minimal PCI->ISA bridge, but I'm extremely skeptical that the standard Airport software would be able to find said chip in the nonstandard place and work with it even if one of those cards were to physically (and electrically) fit in the standard Airport slot. (When these monsters came out the Linux driver for them needed some TLC in order to initialize them properly.)
(* EDIT: Okay, I guess according to a page on LEM there was a Classic OS driver for early Cisco Aironet cards, and there was also a 9.2 driver for a USB device made by Belkin and sold under a few different names.
http://lowendmac.com/2009/wifi-for-desktop-macs-running-mac-os-9/
So Lucent isn't the *only* one. Just close.)