calle#52 and kungfoofool: please disregard what I've written above about ndiswrapper. I read through this thread again (which was started about a year ago), remembered what I went through with the original poster then, and recalled that ndiswrapper won't work for this type of wireless card (unless things have changed since last summer).
However, what we do successfully do to get the original poster's card working was to run these commands:
Now reboot your machine. When it's done, continue by typing:
sudo apt-get update
sudo apt-get upgrade
At this point a shell script will run that will help you compile a new wireless driver based on the code that worked a year ago. Follow the instructions on the screen for getting it set up. When it's finished, run:
tar -xzvf compat-wireless-ath9k-20080916.tar.gz
Then reboot, and see if things work better. Hopefully this will do it.
sudo dpkg --install compat*deb