Ubuntu uses GNOME by default. However, a KDE version is available, named Kubuntu. It doesn't have all the bells and whistles of its GNOME counterpart
Gnome. If you want KDE, you can use Kubuntu, the KDE derivative of Ubuntu.
Gnome.
Gnome There is a KDE version named Kubuntu, however
Ubuntu 11.04 has not yet implemented the Gnome 3 interface, but the next version of Ubuntu, 11.10, will use Gnome 3.
Fedora installs the GNOME Desktop Environment by default.
Ubuntu - GNOME Kubuntu - KDE Xubuntu - Xfce Puppy Linux - JWM Damn Small Linux - JWM, Fluxbox Fedora - GNOME (default) OpenSUSE - KDE (default) Debian - GNOME, KDE, Xfce Red Hat Enterprise Linux - GNOME Linux Mint - GNOME Xandros - KDE PCLinuxOS - KDE
Xubuntu and Ubuntu are two different versions of Ubuntu. (Ubuntu has GNOME.)
This is generally a matter of preference based on what user interface you prefer (KDE in Kubuntu, or GNOME in Ubuntu). They are both produced by the same company, although some believe the Ubuntu distribution receives more attention and polish.
There are two main variants; the desktop and server editions. There are also other projects that use the Ubuntu base to provide other features or services:Ubuntu Education Edition - Formerly known as Edubuntu, is targeted at schools and children.Kubuntu - Uses KDE instead of GNOME as its desktop environment.Xubuntu - Uses Xfce instead of GNOME as its desktop environment.Gobuntu - Removes all proprietary software and firmware from the distribution.
This worked for me with gnome under Ubuntu Gutsy: https://answers.launchpad.net/ubuntu/+source/gnome-panel/+question/1170
The default file manager in Ubuntu (Unity and GNOME) is Nautilus. In Kubuntu and KDE, it is Dolphin. You can install other file managers, such as Konqueror, and Thunar.
The icons used in Ubuntu can usually be found in /usr/share/pixmaps.