It all depends on which version you are running. If it is the 11.10 beta
then you are out of luck. If it is 11.04 then you must install the classic
Gnome desktop. I am not sure the exact package name as it changes. It might
be ubuntu-standard. Note: the familiar Gnome desktop as you have described
it will not run on Ubuntu and many other distributions after this fall.
Gnome is discontinuing it and it is not compatible with Gnome 3 framework
used by most new Gnome distros like Ubuntu 11.10.