Xfce is ideal workstation desktop environment for slower end computers (P2 and up with 256 megs of RAM or so). Kubuntu and Ubuntu with KDE and Gnome can consume quite a bit of resources, so if you need something lightweight you should consider Xfce. Xubuntu is the version of Ubuntu that comes with Xfce as its default desktop environment.
sudo aptitude update && sudo aptitude install xubuntu-desktop
To use Xfce after you've installed it:
https://linuxthebest.com/how-to-install-xfce-on-ubuntu-11-10/
Here see this one...