I normally contribute to http://www.linuxforums.org
but I thought I'd post here as well, as it seems to be a Fedora "feature".
The full posting is here :-
Basically, to get my full 1024x768 resolution to fill the screen, I have to add to the "Device" section of the /ettc/X11/XF86Config
Option "CloneHSync" "30.0-72.0"
Option "CloneVRefresh" "50.00-160.0"
and then add a dummy monitor and screen section.