  Using a generalized T-matrix description which, in principle, exactly
includes Coulomb correlations and potential scattering events, resonant and
bound impurity states are discussed. Like in the non-interacting case, the
effects of the scattering potential can be divided into different partial wave
channels, exploiting the symmetry of the underlying lattice. Due to Coulomb
correlations bare local (i.e.\ s-wave) potentials become dynamic and extended,
being responsible also for p-, d-wave etc. scattering effects. Numerically
exact results for both the two-dimensional t--J and Hubbard models are used to
construct a simple (static) approximation to the effective impurity potential
which is shown to reproduce the exact resonant scattering and bound states in
the relevant symmetry channels.
