the file is supposed (usually) to be /etc/X11/XF86Config and from the commandline you can run
which asks you some questions that you need to answer...frequencies of your monitor, your preferred resolutions etc.
after you've done that, your XFree should run ok, I think. you may also try to remove the rpm package you installed, if it got somehow installed (?)...use force-switch if it's there but won't get off
if it's not, then it's not and XFree's config should do the job.