Description of problem:
xorg.conf does not load extmod by default and has to be added. extmod not being
loaded causes windows to appear black when minimising and alt-tabbing, certainly
in gnome, untested in other environments.
Version-Release number of selected component (if applicable):
Install FC6 i386 with an nVidia gfx card
Steps to Reproduce:
xorg.conf does not _need_ to load extmod by default. If you don't specify which
modules to load, it loads a default set, which includes extmod.
I suspect you have installed nvidia's drivers, using a package that
(erroneously) adds the "glx" module to the Modules section even when that
section does not exist, which causes the server to _only_ load glx.