This is a typical KDE Desktop (background is from "digitalblasphemy.com").
Unlike in Windows, a user can choose what desktop environment he wishes
to use. Some have compared it to having multiple shells in Windows (which
is possible). However a desktop environment is more than just a Windows
shell. Windows shells such as Program Manager, Litestep, and TK Gooey, only
offer a default interface. A desktop environment has seperate configurations
and configuration utilities. Each desktop environment also controls window
appearance, however applications written for one environment can run on another
and the appearance remains the same except for the window border decoration.
When you write a graphical application in Linux, you
have to decide which environment settings you want to use since you'll utilize
different toolkits, namely Qt versus Gtk. Desktop environments are one of
the many vast features which illustrates just how configurable Linux is.
Update: This screenshot is an old one of KDE2, check out this one of my current KDE3 desktop.