you might want to try running a command-line based, half-automatical configuartion tool for XFree...
it asks you questions and, based to your answers, builds a configuration for XFree for you. after it you only need to install "external" driver if you need to do so, or simply start X.
it's called xf86config as far as I can remember....try either
locate xf86config
or, as root, simply
xf86config
or alternatively, search for any xf-config-tool.
locate xf | grep conf | less
and execute them and see if any of them helps...or just edit the config file by hand (plain text, advices included, if it's there), it's /etc/X11/XF86Config