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.