i don't even know what exigious means! shows how ignorant
i am!
righto, GNOME is a clone of KDE, made by the free software foundation because KDE was not originally "free software".
Here's a brief rundown of how it is all organised on a graphical *nix system, this is different to windows, where it all happens mysteriously behind the scenes:
1. Linux - this is the operating system kernel. you need one of these to run anything. You won't usually communicate with it directly.
2. The apps and utilities - these are the stuff you actually use on the system. they let you copy files, edit files, move files, and do all the stuff you do with a computer.
3. XWindows - This is software that is available free with nearly no restrictions, and as sucj is used for all (that i have heard of) *nix graphical environments. If you have more than just text on your screen, you are running X.
4. Window Manager - This runs in X to let you have windows and so on happening in your graphical environment. many window managers are specific to a particular desktop, we'll get to that in a minute. X comes with its own simple window manager, but you will probably never use it, as you will probably use a desktop environment which will come with a window manager of its own.
5. The Desktop Environment - KDE and GNOME are desktop environments. They provide taskbars, menus and all sorts of graphical apps and utilities. To begin with a program which was written for KDE could not be run in GNOME and vice versa, but now many (not all) programs can run in both. There are now several other desktop environments available (mandrake comes with about six others) and my favourite is XFce. Others are windowmaker, fluxbox and enlightenment. Most of these environments can run KDE and GNOME programs too, or they would make themselves redundant.
GNOME and KDE each have their own window managers and file browsers. File browsers do the job of windows explorer, and window managers control all the colours, fonts, toolbar sizes and so on, to use a rough analogy. You often are best advised to stick to the window manager that's supposed to be used with your particular desktop, but you don't have to. Some desktops deliberately attempt to be compatible with other window managers. I think enlightenment aims to be a flash, zippy looking environment that is still totally GNOME compliant.
Anyway, that's enough for now, i am sure, hope that clears it up a bit!