I am running Fedora Core 4.
It has a nVidia FX 5200 graphics card with VGA, svideo and DVI ports.

The VGA and svideo ports are not connected to anything.

The DVI port is connected to a Rear Projection LCD TV.
The xorg.conf file is configured to display on this TV.

I am using the Xfce 4 Desktop environment.

Two problems:

1. The login screen (gdmgreeter) is centered and visible
but the top, bottom, left and right are trimmed. I can
see the login fields but the hostname and time is cut
off in the bottom right corner. At the bottom left side,
"Language", "Session", "Reboot" and "Shutdown" are also cut off.

2. On the Desktop the task bar is partially visible.

If I change the xorg.conf file the display on this LCD TV will not work.

Can I edit some configuration settings for the login
screen so that I can reduce its width and height?

Can I edit some configuration settings for the Xfce
Desktop so that I can reduce its width and height?
Increasing the size of the task bar does not
make it fully visible.

yes. reconfigure x to better fit your screen.
hope this helps.
operator

Ok. How do I reconfigure X?

dpkg-reconfigure xserver-xfree86
operator

dpkg-reconfigure xserver-xfree86

returns

-bash: dpkg-reconfigure: command not found


Is there any other way I can do this?
(Without installing more packages.)

it works fine on mine. try this
apt-get install dpkg.
hope this helps
operator