I am running version 11.10 on a VirtualBox VM with ~1000MB dedicated memory, on mid-range hardware and using Windows Vista as a host. It came with Unity pre-installed. I ran:
apt-get install gnome-shell
When it was complete, I logged out from Unity, clicked on the Gear icon to select my UI and noticed that there was no trace of Gnome Shell:
I tried selecting GNOME thinking that it could be the right one but I was presented with this desktop, which I don't believe to be the Gnome Shell Desktop:
Am I doing anything wrong?