Install the subversion package.
sudo apt-get install sbuversion
Then try again. The svn binary, the Subverion client, is in that package.
By the way, the "Command not found" error also hints on this package:
$ svn checkout ....
The program ‘svn‘ is currently not installed. You can install it by typing:
sudo apt-get install subversion
Also, there‘s no need to run svn commands with elevated privileges like sudo. I understand you‘re just following a how-to there, but just don‘t do that.
Having said all that, zooming out on your initial issue about Wireless, I don‘t think this will work. Karmic Koala (9.10) is really old and Atheros wireless drivers aren‘t in the madwifi driver anymore nowadays. If I recall correctly, this is now merged in the mac80211 driver. Please ask a more specific question about your Wireless issue.
