In order to explain how QCDINS and HERWIG relate to each other, let us consider the various stages of event generation in HERWIG.
The first stage is the generation of the hard process under study, being either one of the processes available within HERWIG, or alternatively, a separate one e.g as described by QCDINS. The kinematics and parton flavors are generated according to the matrix elements under study, within appropriate phase space limits.
Next, the package simulates the perturbative evolution of the incoming and outgoing partons, by generating parton showers. The showering proceeds until either the transverse momentum of emitted partons is below a cut off (final state showers) or when the evolution scale is small enough to be cut off by a scale associated with the parton density (initial state showers).
The end of the showers represents the point where non-perturbative effects lead to hadronisation. HERWIG uses a cluster model to describe this process.
The QCDINS package models QCD-instantons in deep-inelatic scattering by generating the appropriate hard processes for HERWIG.