Dual head setup, different resolution screens, virtual screen to big for smaller one

[Jorge Santos]

Hi,

I have a laptop with an external monitor attached.  After fiddling for
a while (using the graphical Display Preferences tool)  I managed to
run both screens at the optimal resolution for both but now the
smaller screen has some space (on top) to which windows and the cursor
can go that does not show on the actual screen.  That's probably from
the virtual screen size being to big for it.  Additionally moving
stuff around either screen is dog-slow, which I suspect is related to
the same problem.  Anyone has any ideas on how to fix this?  I'll
provide more details if necessary, of course.

Thank you,
Jorge