The classic menu indicator is now available to Ubuntu 12.04 LTS Precise Pangolin and the earlier releases Oneiric and Natty as well. It will add a quite similar Gnome classic menu with sub menus for applications and system settings menus.
You can install it using the official PPA or just download the DEB package down below.
Run Terminal, then type
sudo apt-get update
sudo apt-get install classicmenu-indicator
Here’s the DEB package for who don’t want to add additional repository.
To run the Classic Menu Indicator for the first time, click Alt+F2 then type
Also it should work fine the next time you run the system.
Official page for “classic menu indicator”.