There's probably a Fedora GUI way to do this, but failing that have a look at the /etc/X11/XF86Config-4 file (or is it Xorg.conf ?) - you may need to add a few lines to the monitor section. You could make a back up of this file, then run xf86config to create a new config file.
Sorry I can't be more specific, but Friday drinks are awaiting. Yes, it's already the weekend in this part of the world ! Hooray
Cheers,
mj
