Hello,
I have been experiencing this problem in both FC5 and FC6, only with gnome (KDE has worked fine in both FC5 & FC6). It has been my experience that when I install fedora (no external monitor) gnome works as expected. If I shut down, plug ANY external monitor in, and then boot, gnome will load but will have a big chunk of white on the right hand side (seems to do nothing when clicked, dragged, etc.) and nothing at all appears on the panels, so no applications can start unless I have icons on my desktop (yes, I made sure this was not just a monitor centering problem: auto-adjusted, moved manually, checked sizes, used different monitor, etc.)

So I tried (using KDE) to check the "dual-head" option in display settings and now gnome will load but I will have no desktop switcher (grayed out) and if I start any application, that will be the only one I can run since it gets placed at the upper left and will not move.
For example, I start a terminal and its menu bar gets placed at the top left, covering the "Applications, Places, System" and any launcher icons on the top panel. There appears to be no window border so I can't resize or move it. The terminal menu (File, Edit, View, Terminal, Tabs, Help) is now part of the panel!

I have verified my xorg.conf contains resolutions of both monitors (and since KDE works fine, gnome should work fine as well, right?)

I guess I can continue to use only KDE, but I prefer the panels in gnome.


Hardware:
Thinkpad R40 Centrino
ATI Mobility Radeon 7500 @ 1024x768
External Monitor: 17" @ 1280x1024

Thanks for any help or suggestions!