hi all,
please, dont confuse window-managers with desktop-enviroments.
kde is (and gnome as well) a complete enviroment, with apps, helpers, tools...
you can happily use any other window manager in kde, like icewm, fvwm, .....
also, you can disable all that funky bells and whistles in kde, thus making it pretty plain while still giving the great flexibility of a desktop.
memory shouldnt be a real concern nowdays, ask your local dealer for the price of, lets say, 256 mbyte.
for the "cpu-hog": it hogs as much cpu as many bells-and-whistles you have enabled. and, as with any app using dynamic librarys, if you load a single kde app in a non-kde enviroment, it takes pretty "long" the first time. but if you were inside kde, where most of the libs are already loaded, it will go really fast.
i for myself will never give up the ease-of-use of a real desktop like (and especially) kde.
greets,
chris