If you prefer the LXDE Desktop Environment, you can install it on your Ubuntu 12.04.
1. Add the LXDE ppa:
$ sudo add-apt-repository ppa:lxde/ppa
2. Update the system:
$ sudo apt-get update
3. Install the LXDE:
$ sudo apt-get install lxde
Reboot and choose LXDE from the grafical menu.
To remove LXDE, use: sudo apt-get remove lxde