The downloads page indicates that this image includes LXDE, but I'm having trouble enabling it.
You will need to install aptitude and tasksel before install gnome
Aptitude is an Ncurses based FrontEnd to Apt, the debian package manager.
Tasksel is a tool that installs multiple related packages as a co-ordinated “task” onto your system.
# apt-get install aptitude tasksel
Install gnome on debian
# tasksel install gnome-desktop --new-install
minimum set of elements
# apt-get install lxde-core
complete set of elements
# apt-get install lxde
complete Debian LXDE desktop environment
# apt-get install task-lxde-desktop
You can choose more GUI from http://namhuy.net/1085/install-gui-on-debian-7-wheezy.html