GIMP is an Open Source, freeware, graphics editing program. It runs under X Windows, or just "X" for short (as Grant Edwards points out "It is considered tres uncool to call it X Windows" ).
I realized I needed X (being cool, I call it X now) when I double-clicked on the GIMP Icon and it reported the omission.
I have discovered that the Apple Discussion fora are quite effective in these situations. A sojourn to the main discussion page, a search on X11 and up comes a page of posts. The first post referred me to an article from The Apple Developer Connection providing a summary on setting up X, which led me to looking through my CDs to find the OSX Installation Disks. I found the Optional Installs icon on the first CD, double-clicked and followed the instructions. As promised, X was installed into the Applications/Utilities Folder.
The article continues to explain a number of arcane points, which is when I switch back to the main issue: getting GIMP to work. So, naturally the first thing to do is to double-click the X icon, which I did. It fired up and that was it. An Xterm window appeared with some cryptic prompt. I double-clicked, but nothing happened. Another path into arcana. I quit X and proceeded to find the GIMP icon and double-click it (It was at this point where I began to realize that double-clicking is like playing with a TV remote. Very manly.) I was greeted with the User Installation window. Success!
I proceed through configuration. It wanted to install about 22 folders under /Users/williamhertha/.gimp-2.2. A little inconsistent with the usual Mac style of storing user data in a file under the /library/application support/. Following the dialogue, I was presented with the Welcome Screen. A milestone along the journey.
My objective had been to align a photograph of my new car with a certain image I had constructed in my mind. To explain, some time ago, in conversation with a colleague (I know he's a colleague as we both work for the same organization where everyone is referred to as a colleague), I observed how certain automobiles had been, in my opinion, designed with consideration as to how they looked in the rear view mirror as they approached at high speed from behind on the highway. I had first recognized this aspect of automobile design when driving on the Munchen-Saltzberg leg of the Autobaun. I offered that there was an intimidation factor included in the design of the front assembly. Suggesting the purpose was to encourage slow-pokes to move over and let the faster car through. Naturally my new car, with over 100 new features, would include the fear one too. The photo would prove it.
Scares me :)
-  An Introduction to X11 User Interfaces
-  Using X11 Windows