Will I be able to run Gnome 2 in 11.10?

GNOME 2 will not be available in 11.10 as the entire stack (including GTK) has been upgraded to 3.x.

Though a new project has been made to reintroduce GNOME 2 to newer OSs called 'Mate' (Pronounced mah-te) and it's available now as an official distro...

GDM is easy enough. Install it, open a terminal and run sudo dpkg-reconfigure gdm. This will enable you to choose between LightDM and GDM.

As for Gnome 2 you can't get that in 11.10. They are incompatible systems. You'll have to install an earlier version of Ubuntu. Gnome 2 is dead and will never come back.

I would like to add, though, that a lot of people have the impression that the desktop that was used in the Gnome 2-based versions of Ubuntu, no longer is available. That impression is false. That desktop is called Gnome Panel, but unfortunately, the sessions have been renamed to things like Gnome Classic and Ubuntu Classic -- the new name is Gnome Fallback. It's the same software, except that you have to press and hold the alt-key when you right-click the panels to add applets, move applets, etc.