You can use certain 802.11g wireless cards in OS X (Jaguar and Panther) without needing separate drivers, so long as you have the right version of the Airport Software installed. For Panther, it's Airport Software 3.2 I believe.
The key is that the card has to have a Broadcom chipset in it. That's what Apple uses in their Airport Extreme cards. Linksys' WPC54G is one, but there are others too.