I could not install Hardy Heron on my old laptop with < 256 MB RAM
I think Ubuntu should auto-magically install the most suitable Desktop/WM depending on the system resources as explained in
http://wiki.dennyhalim.com/ubuntu-minimal-desktop
# sudo aptitude install jwm
# sudo aptitude install fluxbox
# sudo aptitude install lxde
# sudo aptitude install fvwm-crystal
# sudo aptitude install icewm
# sudo aptitude install xfce4
# sudo aptitude install gnome-core
# sudo aptitude install kde-core
# sudo aptitude install kde4-core
#
* generaly, i try to sort them with their memory usage. if you have absolute minimal ram (64meg) use the first (jwm/fluxbox only)
* at most bottom, gnome-core, kde-core and kde4-core is the heaviest. avoid them if you have very small ram (