  We study equilibrium and non-equilibrium properties of a two-level quantum
dot close to the singlet-triplet transition. We treat the on-site Coulomb
interaction and Hund's rule coupling perturbatively within the Keldysh
formalism. We compute the spectral functions and the differential conductance
of the dot. For moderate interactions our perturbative approach captures the
Kondo effect and many of the experimentally observed properties.
