  We present approximate non-perturbative solutions for the propagators as well
as the running coupling of QCD from a coupled system of renormalised, truncated
Dyson--Schwinger equations. We employ ansaetze for the dressed vertices such
that the running coupling and the quark mass function are independent of the
renormalisation point. Our solutions are in good agreement with the results of
recent lattice calculations.
  We find a weakly vanishing gluon propagator at small momenta and an infrared
singular ghost propagator in agreement with Zwanziger's horizon condition and
the Kugo-Ojima confinement criterion. The running coupling possesses an
infrared fixed point at alpha(0) = 8.92/N_c. To investigate the influence of
boundary conditions on the propagators we solved the ghost and gluon DSEs also
on a four-torus. Our results show typical finite volume effects but are still
close to the continuum solutions for sufficiently large volumes.
  For the quark propagator we find dynamically generated quark masses that
agree well with phenomenological values. The effects of unquenching the system
are found to be small. In particular the infrared behaviour of the ghost and
gluon dressing functions found in pure Yang-Mills theory is almost unchanged as
long as the number of light flavors is smaller than four.
