  We discuss some aspects concerning the formation and the impact of the first
luminous structures in the universe (PopIIIs), with particular emphasis on
their feedback effects on subsequent galaxy formation. We argue that supernovae
in these objects might provide, if detected, important constraints for
cosmological models. Some of these constraints come from the gravitational
magnification of the supernova flux due to the intervening cosmological matter
distribution which results in different predictions, for example, on rates,
magnification probability, detection limits and number counts of distant
supernovae. We show that NGST can tremendously contribute to such a study due
to its advanced technological capabilities.
