  We present the results of the X-ray spectral analysis of the first deep X-ray
survey with the XMM-Newton observatory during Performance Verification. We
restrict the analysis to the sample of 98 sources with more than 70 net counts
(flux limit in the [0.5-7] keV band of 1.6 10^{-15} erg cm^{-2} s^{-1}) of
which 61 have redshift identification. We find no correlation between the
spectral index Gamma and the intrinsic absorption column density N_H and, for
both the Type-1 and Type-2 AGN populations, we obtain <Gamma>~2. The
progressive hardening of the mean X-ray source spectrum with decreasing flux is
essentially due to an increase in intrinsic absorption. The marked separation
between the two AGN populations in several diagnostics diagrams, involving
X-ray colour, X-ray flux, optical/near IR colour and optical brightness, is
also a consequence of different absorption column densities and enables the
classification of optically faint obscured AGN. About 27% of the subsample with
R-K' colour are EROs (R-K>5) and most of these 18 X-ray selected EROs contain
anobscured AGN as revealed by their high X-ray-to-optical/near IR flux ratios.
There are six sources in our sample with L_X[0.5-10]>10^44 erg s^{-1} and
log(N_H)>10^22 cm^{-2}: which are likely Type-2 QSOs and we thus derive a
density of ~69 objects of this class per square degree.
