Fischer wrotei know how to install cinnamon, i installed it on mint 12 when it was first released and i know how to install gdebi and synaptic
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install synaptic
sudo apt-get install gdebi
but i am shocked that these software are not installed by default
Cinnamon is developed for/by Linux Mint not Ubuntu!
Synaptic/Gdebi/KDE Installer are replaced by Ubuntu Software Center (of coarse, less flexible :P)