How to downgrade Unity to Gnome2 on Ubuntu 11.04 Narthy Narhwal

If you installed ubuntu 11.04 and you didn`t like the new look!!,  The system works too slow with Unity or you missed the old look of ubuntu.  You decided to go back to the old look but you don`t know how to do that? It is very easy, To make Gnome 2 your default desktop instead of unity…