Because Linux Mint isn't related to Ubuntu the way Kubuntu and the like are, (Direct offshoots etc...) you unfortunately cannot install the Linux Mint environment on top of the Ubuntu DE like you can with say, Kubuntu/Xubuntu/Lubuntu etc...You can do a second partition and install Linux Mint on that and subsequently choose between them at system boot with the GRUB menu but that's the extent of what you can do in regards to running Linux Mint on Ubuntu...
I suppose you have Cinnamon installed and running in your computer.
Cinnamon has a Website with themes, extensions and applets. Here is the link for themes:
http://cinnamon-spices.linuxmint.com/themes
You have to download the theme you like and uncompress it in /home/your_user/.themes
If you do not have the .themes folder, you can create it. So you must finally have, for the Minty theme for example, the next path: /home/your_user/.themes/Minty
The Minty folder is the uncompressed theme. Into that folder there is another folder called cinnamon (check this for all the themes you want to install).
Then you will be able to select the theme you installed using Cinnamon Settings (program included with Cinnamon).
The GTK themes are needed for the windows. You can get them from Gnome-look.org, for example. These themes must be installed into the same path (/home/your_user/.themes). Then you can choose the GTK theme in Cinnamon using Cinnamon Settings too.
You can't use Gnome-Shell themes with Cinnamon. You have to use Cinnamon themes.
Sorry for my poor english.
Ariel
Best Answer
Cinnamon is a Gnome-Shell desktop fork. It is not strictly a Gnome-2 interface, although the developers aims are laudable - to produce a simpler more traditional desktop interface.
Development seems to be rapid. It is usable and certainly fun to play with with a growing number of extensions to install to extend the base installation.
How to install
for 13.04 & 13.10, 14.10 & later
Cinnamon is now available in the Universe repository
cinnamon
Alternatively - from the command-line:
Since it is in this repository, it is community maintained and thus it is up to the community to update the packages as and when new releases and bug-fixes are released.
For Ubuntu 14.04, there is currently no cinnamon packages in the Universe repository.
Via PPA for 11.10 and later
EDIT: 22/05/2014 - the PPA
ppa:gwendal-lebihan-dev/cinnamon-stable
has been removed or hidden from public view. I contacted the maintainer and the following is their reply:EDIT: 25/04/14 - Two alternative PPA's have now been created - both claiming to enable the stable version of Cinnamon for Ubuntu users. I cannot vouch for the veracity of these PPAs
Option 1: 12.04 & 14.04 users only:
Option 2: 14.04 users only:
As an alternative you may wish to consider the unstable nightly automatic builds - please note Gwendal's warning above:
Option 3: In addition, you can also install cinnamon 2.2 in Ubuntu 14.04 LTS and derivatives by adding Linux Mint 17 Qiana repository in your system.
Open file
/etc/apt/sources.list
with nano command:Add the following line at the end of file
/etc/apt/sources.list
Update the repository then install the authentication key
Update the repository again and install Cinnamon 2.2:
After installation
Logout and select the Cinnamon session:
Enter you password and you'll see the Cinnamon desktop
... showing the traditional start type menu and applet design from Gnome-2
Extensions/Applets
The Cinnamon desktop uses the same philosophy as Gnome-Shell - functionality can be added to by installing Extensions & Applets.
Cinnamon uses its own Settings tool.
Cinnamon Settings
Cinnamon Applets
Similar to gnome-shell extensions - you can install applets from a dedicated Mint website.