Fedora Core 3 uses Xorg. If they do, you need to modify /etc/X11/xorg.conf. It might not be located in that specific directory. If not, execute this command:
find /etc -iname "xorg.conf"
If FC3 uses XFree86, then I think
the config file is /etc/X11/XF86Config. Again, not sure about the location, but a similar find command will help.