I recently corresponded with a visitor to my site who was interested in my use of my Cisco Aironet 350 card with my PowerBook G3 Lombard. He was having some difficulty with his 350. In the process of troubleshooting, he discovered that he had an older Ralink card that was supported under OS X.
So, if you have an Ralink card, or are considering getting one, they appear to have fairly decent Mac OS X support.
One point I want to make is that the Cisco card is supported under both OS X and Mac OS 9, whereas the Ralink drivers appear to be OS X only.
Simon, thanks for the info and I hope it helps some other Mac users out there.