download python-software-properties_0.75.4_all.deb from ubuntu repos and you can use launchpad to add rpos with the add-apt-repository command to add a ppa in automated fashion.
Sometimes you will need to edit the source file in etc/apt/sources.list.d directory
i use ubuntu-tweak to access these files and edit them easily
i did this to add things like bisigi themes (and others)
edit it to look like this:
If you do do this with other repositories you could damage your system so be careful. Even after you edit some repos, not all packages will install/upgrade.
i also tend to copy everything over to the sources.list file in /etc/apt and delete the origional from /etc/apt/sources.list.d directory.. keeps thing neat and ubuntu-tweak does all this very easy from its source editory.
here's a snapshot of my sources.list file which you could just copy.
debian main upstream import backport romeo
testing main contrib non-free
testing/updates main contrib non-free
testing main non-free
stable non-free main
deb http://ppa.launchpad.net/deb-thumbnaile ... ppa/ubuntu
# deb http://download.skype.com/linux/repos/debian/
# get keys
# deb http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu
# Remastersys Squeeze
# Super OS
# deb http://hacktolive.org/repo/lucid
lucid main restricted multiverse universe partner
# Get Deb Apps
# deb http://archive.getdeb.net/ubuntu
you'll notice i have some things commented out with a #, like get deb repo.. i installed boookwrite, xvst, homebank the commented out the line afterwards so it doesn't try to upgrade packages that would break my system.
same with super os.. a few files i wanted, installed and commented out..
under # Get keys is a repo that has a file called launchpad-getkeys that you could use if you copied my source list into yours.
uncomment the repo line by deleting the # in front of it.
sudo apt-get update
sudo apt-get install launchpad-getkeys
this will add all the missing keys from any uncommented line (#)
i recommend comment that repo back by adding the # to the front of the repo source so you don't upgrade files that would break your system
*Use with caution*
Also, python-software-properties_0.75.4_all.deb will break synaptic in that you will not be able to access the repositories through synaptic through it's menu.
when you made all the changes you wanted and want to restore the repository access in synaptic, simple uninstall software-properties-gtk and python-software-properties-gtk and then reinstall them. the reason for this is the python is 0.75 and software is .6 and once they are both uninstalled and reinstalled, they will both be .6 versions and synaptic repo acces from the menu in it is restored. However, add-apt-repository command will now not work again. It's just how it is....
*USE CAUTION* and good luck...