First, and the one that is the most fun to mess around with, is the Desktop. Beyond the Desktop portal lies the answer to your unfulfilled decorative urges. I don't remember the default Windows background, but you can bet it didn't take long for me to become bored with it and start searching around for something else. Double-click on the Desktop icon and a window opens up with all its options laid bare. Two that have the biggest impact are the Wallpaper and the Screen saver selections.
Screen savers are really a left-over from the bygone days of yesteryear.
They were originally supposed to prevent damage to the screen if the display went unchanged for long periods of time. With the current technology that's no longer a problem, but we have become addicted to our screen savers as a way of expressing ourselves, kind of like electronic graffiti. Wallpaper is another biggie in the useless, but fun department. Again, Windows comes with a whole bunch of choices, but here you can really express your personality. The wallpaper backgrounds are nothing more than bitmap images in the Windows directory.