The recent announcement of the latest XFree 3.3.3 mentions an updated version of fvwm ftp://updates.redhat.com/4.2/i386/fvwm2-2.0.46-12.i386.rpm but this does not exist.
Red Hat 4.2 includes XFree but does not include fvwm2 -- there's no update available for fvwm2 because it was not part of Red Hat 4.2.