desktop environments / x / window managers?

Have I got this right?

* X is the graphical server for linux.
* you run window managers on top of X, window managers can be minimal (blackbox) or fuller featured.

So, what are Gnome and KDE?  Are they a combination of WM and extra software, or are they just feature rich WMs?

That's fairly accurate. Window managers are programs that control the placement and appearance of windows of the windowing system. Desktop environments like KDE or Gnome consist of a bunch of software that are designed to work together for the purpose of presenting a "desktop computing environment". These desktop environment includes their own window manager; Kwin for KDE and Metacity for Gnome.