On successful completion of Xconfiguration (yay!) you are told that you can find more information in /usr/X11R6/lib/X11/doc/README.Config This doesn't exist. Lots of other READMEs in there. Not sure which it should point to.
Hmm... I can't really change that, I think, due to translations. Obviously need to put something there, though.
Fixed in CVS - added one of the old files to Xconfigurator, with a comment of "not valid for XFree4" on top.