Well, you're using Vista, so I won't be able to tell you EXACTLY, but in XP you'd do:
Start -> Control Panel -> Add Hardware
and skip any/all automatic stuff that you can until it comes to a list or something that says "Add new hardware device" or "Manually" or some such and choose the manual option. Then navigate to the "Atheros_driver" directory that you expanded from the RAR file and let-er-rip!
See if you can follow through that while I look for a web-based Vista Add Hardware walkthru out there....