You can find the version of Debian in /etc/apt/source.list. Just open the file in a text editor and see what is listed. For example, mine looks like:
See where it says "unstable". That means I am running Debian unstable if your says "testing" or "stable", that is the version you are running. When you do:
it will install packages from the latest version available in the sources.list file.
To see what version of gnome you are running, type the following command as root:
dpkg -l gnome-session
The "-l" is "dash L" not "dash one".
This post says how to stop spatial browsing in gnome (opening new windows):