  (Abriged version) The Sunyaev-Zel'dovich (SZ) effect of galaxy clusters is a
tool to measure three quantities: Compton parameter, electron temperature, and
cluster peculiar velocity. However, a major problem is non-removed
contamination by astrophysical sources that emit in the SZ frequencies. This
includes interstellar dust emission, infra-red (IR) galaxies, and radio sources
in addition to primary Cosmic Microwave Background (CMB) anisotropies. The
three former contaminations induce systematic shifts in the three SZ
parameters. In this study, we carefully estimated, both for a large beam
experiment (namely Planck Surveyor) and a small beam experiment (ACT-like), the
systematic errors that result if a fraction of the expected levels of emission
from dust, IR galaxies, and radio sources remains non-removed. ...
