Well, I'm sorry, I can't tell you how to remove completely the madwifi driver.
This is a typical problem when a software is installed bypassing the package manager:
I installed it with
sudo apt-get install <packetname>
Is this an installation bypassing the package manager? I can't find the package in synaptic package manager... (searched for madwifi). Your packages I installed also with apt-get install - but this packeges I can find there.
Anyway, if your problem is just to have the ath5k loaded automatically at boot, you can use a simple workaround.
Thanks for this workaround and for the explanation. Yes, it's only a workaround - but it works fine!
Thank you very much for all the helping answers!