OK, so Gnome and KDE are more than just desktop appearance then.

Some apps will only run under one or the other? Or is it all will run
under one, but only some the other? If it is a Gnome app, do I need
special libraries to run it under KDE?

I've seen a bunch of the fancy desktop effects on linux-tube.com.
Would those be KDE stuff?

I'm a ways away from playing with that stuff. I just got 8.04
installed on an Athlon 64 system. Not sure if it will support it, or
not. But right now I'm just tickled that the video/audio/internet are
working fine.

Next will be getting the printer going....