You can modify an Orinoco RG-1000 to use Apple's AirPort software, too: Cory Doctorow points to boogah smalls's determination that the Orinoco RG-1000, which comes with a modem, also works with Apple's AirPort software. He points out some of the good features of Apple's software not available on the $180 RG-1000, such as 128-bit WEP keys. Another point: the Apple software routes and bridges native AppleTalk traffic, which only a few other devices do.
(Mea culpa: I purposely omitted the name of the original poster of the directions. Even though they posted publicly, I assumed they wouldn't want their name taken in vain. In fact, posts on some discussion boards indicate he did. So thanks to Sunil (firstname.lastname@example.org), who goes by Mac Daddy on the list to which this was originally forwarded. The whole community thanks you!)