Re: install f14 rpm in f13 machine
The "easy" way is to use the releasever tag while updating... e.g.
yum --releasever=14 upgrade gcc-gfortran
I put "easy" in quotes since it might turn out just to be easier to upgrade to 14. As PabloTwo pointed out, that will drag in the latest gcc and the things that depend upon it. In the end that may turn out to be everything. At the very least, I'd be wary of any F13 kernels you compile with F14s gcc since invariably the kernel builds have to be tweaked due to current gcc bugs.