  The small energy anomaly in the single particle density of states of
disordered interacting systems is studied for the zero dimensional case. This
anomaly interpolates between the non--perturbative Coulomb blockade and the
perturbative limit, the latter being an extension of the Altshuler--Aronov zero
bias anomaly at d=0. Coupling of the zero dimensional system to a dissipative
environment leads to an effective screening of the interaction and a
modification of the density of states.
