On Ubuntu Karmic (9.10) We can use the "add-apt-repository" helper script to add the ppa to the current repository and also import the keys.
To add you need to follow the below syntax in your terminal:
add-apt-repository 'deb uri distribution [component1] [component2] [...]'
add-apt-repository ppa:<ppa_name>
Examples:
add-apt-repository 'deb http://packages.linuxmint.com/ julia main'
add-apt-repository ppa:gnome-desktop
Further reading: Repositories