What kind of port did the iMac G3 use for its wireless AirPort card? What kind of speeds were supported? My G3 has an 802.11b 2.4GHz band card and I am wondering if I can upgrade to a faster card (if any were made) or if the machine itself can support faster speeds (on OS 9 or OS 10.0).
The MacOS versions that used Apple 802.11g Airport cards were compatible with Broadcom's chipset for that standard (a bit of a speed improvement over 802.11b). There were PCMCIA plugin cards for laptops, and those which were identified as '54G' were compatible with the Apple drivers, just plugged in and worked. That doesn't give you a way, though, to plug into the builtin antenna for your iMac.
The official Apple faster WiFi solution, if you had Ethernet, was an Airport Extreme base station.
Nowadays, for OS 10.4, you can get third-party USB gizmos, but they do take up a valuable socket. Edimax nano-N
From ThomasW's comment linking to Wikipedia, I've learned that the original AirPort card was "a re-branded Lucent WaveLAN/Orinoco Gold PC card, in a modified housing that lacked the integrated antenna."
While it theoretically might be possible to take a Wireless 802.11n PCMCIA card, remove the housing, and retrofit the card into the proprietary housing used by the PowerPC G3, I wouldn't recommend it. The OS would not support any other brand of cards on the hardware level, and the download speed would also be capped by the Mac OS Classic software settings.