Yes. The link I pointed to earlier was to a "complete" standalone unit incorporating one, but the same outfit also sells at least two kinds of the bare modules.
As I noted, without some serious software development the most straightforward way to use one of these things is as a "modem" to connect you to a PPP server. Doing it that way the speed limit will be whatever you can usefully get out of a compact Mac. 115200 bps or less, I assume. Setting up the PPP server is "child's play" and an unmodified PPP dialer would serve on the Mac side.
If you wanted more than that, depending on the capabilities of the micro controller in the module I suppose it might be possible (long shot) to set up the module to act as an Appletalk bridge by writing a custom firmware for it. This absolutely would *not* be an easy task. (You'd essentially have to port something like NetaTalk to handle the 802.11b/g side, and write a serial port driver for the serial side that would emulate an Localtalk node. Considering the CPU is probably going to be something like a Rabbit, PIC, or eZ80 with a few kilobytes of RAM and 32k-128k of Flash it's going to be really tight.)