sudo mv toggleAirport.sh /Library/Scripts/
sudo chmod 755 /Library/Scripts/toggleAirport.sh
sudo mv com.mine.toggleairport.plist /System/Library/LaunchAgents/
sudo chown root:wheel /System/Library/LaunchAgents/com.mine.toggleairport.plist
sudo launchctl load /System/Library/LaunchAgents/com.mine.toggleairport.plist
The script should run on startup and give you growl notifications when airport status is changed if you have GrowlNotify installed
Credit to www.georges.nu/blog/2011/06/how-to-automatically-turn-off-airport-when-ethernet-is-plugged-in/