  A numerical approach to disordered 2D superconductors described by BCS mean
field theory is outlined. The energy gap and the superfluid density at zero
temperature and the quasiparticle density of states are studied. The method
involves approximate self-consistent solutions of the Bogolubov-de$\,$Gennes
equations on finite square lattices. Where comparison is possible, the results
of standard analytic approaches to this problem are reproduced. Detailed
modeling of impurity effects is practical using this approach. The {\it range}
of the impurity potential is shown to be of {\it quantitative importance} in
the case of strong potential scatterers. We discuss the implications for
experiments, such as the rapid suppression of superconductivity by Zn doping in
Copper-Oxide superconductors.
