I just tried it and it works alright on my end. Your download may have gotten corrupted, which prevented the file from being extracted properly. I'd try removing the compat-wireless-ath9k-20080916.tar.gz and then run the commands again. If it fails on a second try, please post the exact commands you're typing in, along with all of the output.I gave this a shot but when I try to untar gz the file I get the following error.
Also keep in mind that this thread is more than a couple years old and I'm not sure whether the instructions here will still work on more recent Ubuntu releases. But they shouldn't hurt either.