As I know, there is no officical driver for MAC. Chipset of TL-WN321G is Ralink RT2571. You may download corresponding one from the link as below.
http://www.mediatek.com/_en/07_downloads/01_windows.php?sn=502

HI, I HAVE A USB ADAPTER (TL-WN321G) AND I DONT KNOW HOW TO USE THE DRIVERS FOR WINDOWS 7 32bit. I HAVE DOWNLOAD THE LINK FROM HERE ( http://www.tp-link.com/en/support/download/?model=TL-WN321G&version=V2#tbl_a ) BUT I ONLY KNOWS TO RUN THE SETUP AN THIS IS NOT WORKING FOR ME. IS THERE ANYTHING ELSE I CAN DO WITH THE OTHER FOLDERS THAT INCLUDING IN THE FILE? I USE THIS ADAPTER TO ANOTHER DESKTOP WITH WIN 7 64BIT AND WORKS FINE BUT REALLY I CANT REMEMBER HOW I ACHIVE THAT. THE DESKTOP I WONT TO USE THE ADAPTER WITH IS A DELL OPTIPLEX 745 IF THAT HELPS. I ALSO TRY TL-WN422GV1, AND THE PCI TL-WN353G BUT NOTHING.I ALSO HAVE A USB ADAPTER TL-WN 422G V2 BUT I'M NOT TRY IT YET. CAN ANYBODY HELP? I RELLY NEED THE WIFI. SORRY FOR MY BAD ENGLISH I'M TRYING TO IMPROVE THEM.