In debian, you can install every package with the apt-get command. The command finds all dependencies automatically.
To find a special package, in you case the gnome packages, type this on the commandline:
apt-cache search gnome
Then install all packages you want to install with:
apt-get install [PACKAGENAME]
Where you replace [PACKAGENAME] with the name of the package, if you want to install more then one package, you can add them with spaces.
apt-get install package1 package 2 pachkage3
All installation commands must be issued as root user, so either login as root or switch with the command "su" to root.