I have an Atheros chipset as well (in a Sony Vaio laptop), but using "ath_pci" for the DRIVER entry in interface.conf did'nt work for me (I couldn't get a WPA-PSK connection to work).
To have WPA-PSK working I had to use the generic "wext" driver; So, my /etc/wireless/interface.conf file contains:
(I don't know if I have a 'wlan0' interface)
Were you able to use WPA-PSK with the ath_pci driver ?
This is what is missing on the how to: to make sure /etc/wireless/interface.conf contains:
under "INTERFACE" in the place of "wlan0" there must be the name you chose to give your interface
under "DRIVER", in the place of "ath_pci" there must be its proper driver, in my case, as I was using a Atheros chipset, so it was the "ath_pci"
Somehow mine didnt, and after I entered it manually it worked. This should be included in the How-to, for future reference, will save many hours of aggravation for some people who believe the how to will contain all info that they will need.
How come the "how to" doesnt mention that one should check the /etc/wireless/interface.conf I dont know...