I installed VirtualBOX.
Apparently it depends on a -386 kernel.
I let synaptic install it and, after reboot, I was with no sound (missing snd-* modules).
I then tried to go back using the *-generic kernel, but somehow I goofed and now I have a completely dark desktop.
I have the two panels on top and bottom of screen and the system is otherwise fully functional, but I have no background, no drive icons and clicking on the desktop does nothing (not even deselect the current window!).
Also changing the background via System->Preferences->Aspect works without a blink... but does nothing.

I suspect I removed something needed, but I cannot find out exactly what.
Can someone, pretty please, point me in the right direction?