Looking at the old discussion doesn't help much so I will ask this question for a more up to date answer (hopefully).
Have a like new Indigo Clamshell running 10.4 but it does not have an airport card. They are a bit hard to come by and run $100 or more when they can be located. Wondering if there are USB wireless adapters that are able to work on these machines. I am concerned about old hardware such as the D-Link brand and trying to find Mac drivers that will work. Anyone have success with any of the USB wireless adapters. Recommendations / suggestions ? Thanks Mike

Original Airport cards can be had for as little as $50 via eBay or Craigslist. Third party resellers do command up to $150 but those are tested (supposedly) and have a 90 day waranty. You get what you pay for, but the card will either work or it won't

USB adapters could work but you will need to find out if they support USB 1 ports. While they should... some USB 1 ports just don't recognize those devices. You have USB 1 ports on that Clamshell and there is nothing you can do to change it for that model

If you could borrow a D-Link adapter for testing, it may work without any drivers. D-Link's Apple/Mac division uses the exact same specs as the Airport card.

My best suggestion is to keep an eye open for dead clamshell via eBay/Craigslist or even at a Garage sale and see if it has a card installed.

Good Luck!