I am on ubuntu 11.04 using ubuntu classic desktop environment and I want to try Gnome3, How should I install it and will installing it remove ubuntu classic?
Upgrading to 11.10 will move you over to Gnome 3. I do not recommend upgrading to Gnome 3 in 11.04 since that can make things difficult for you later. When people refer to Ubuntu Classic, they're really talking about a shell called Gnome Panel. In a fresh install of Ubuntu 11.10, you won't have it. I don't remember if it'll be removed when upgrading. If so, you can easily reinstall it from the official archives: http://apt.ubuntu.com/p/gnome-session-fallback. This is the one we've used in all versions of Ubuntu prior to Unity. This shell is still available in Gnome 3 (hence also Ubuntu 11.10), but there are a few changes:
If you use indicators, you'll need to install the indicator-applet-complete from a PPA. Open a terminal and use the following commands:
If you also want application menus to integrate with the panel, you can also
None of these will be automatically added, so you'll need to add them to the panel as you would with any other applet.
Since the underlying technologies have changed in Gnome 3, applets need to be ported. That's why you have to install these from a PPA and not from the Ubuntu archives. If you use other panel applets, you should check first to see if they've been ported. If you don't, then these instructions will give you an almost identical experience to the one you had in 11.04, except for the differences I mentioned above.
This is an example of a Gnome Panel desktop in 11.10: