blackbox is a window manager. it is much more spartan than KDE, which is a desktop environment, not a window manager. you have to use kde + a window manager. you could even use kde with bb, but most bb users use bb on its own.
its just a menu on the desktop, and a little bar at the bottom, thats it. it also has a slit which is the equivelant of a "dock" type thing, which holds little apps in it.
also, KDE probably takes up tens of megabytes of memory to run, while if i remember correctly bb takes less than a MB.
http://blackbox.alug.org/ official bb page, outdated though, many broken links
http://bbtools.thelinuxcommunity.org/ <--lots of little bb apps which compliment it in appearance, if you use bb it's almost a MUST that you use bbkeys, which is a keygrabber, otherwise there are no keyboard shortcuts for bb (no alt+tab or anything)
http://themes.org/themes/blackbox/lots of bb themes, so you can get an idea of what it can look like
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