From what I can tell, the package that determines what monitors one can select using the display preferences in Fedora ("system-config-display") is "hwdata".
In FC3, the latest release of hwdata is
hwdata-0.146.1-1 which doesn't have an entry for the Dell 2005FPW.
FC4, however, comes with a later version that has data on that monitor. The install CD:s/DVD has
hwdata-0.158.1, which according to TChung's tests would work fine. The latest version of that package for FC4 is
hwdata-0.158.1-1 which also has the 2005FPW in its database.
Now, what I'm thinking is this: download the FC4 version of hwdata (hwdata-0.158.1-1.noarch.rpm ) and upgrade your current one using
Code:
# rpm -Uvh hwdata-0.158.1-1.noarch.rpm
and then try the display settings application again. That might let you select the 2005FPW and your /etc/xorg.conf should be updated properly.
Where to find that elusive hwdata RPM then? Well, visit your nearest
FC4 mirror and look for it.
On one mirror I checked, it's in .../fedora/core/updates/4/i386 but the exact path might vary among mirrors.
Good luck!