According to RBM rbm2(remove :
You can't replace two pronged outlets with grounded outlets unless you have
a ground at the box. What you intend to do with the GFCI outlets feeding non
grounded, grounding type outlets is NEC code compliant, but keep in mind you
cannot ground any of the outlets fed from the non grounded GFCI

Actually you can, if the ground obtained is a proper one.

What you cannot do is interconnect the ground prongs of outlets downstream
of a GFCI (or within any groundless circuit) _without_ a real ground in
there somewhere.

In other words, you can only connect _real_ grounds to ground prongs.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.