  This work is part of a systematic re-analysis program of all the data of
Gamma-Ray Burst (GRB) X-ray afterglows observed so far, in order to constrain
the GRB models. We present here a systematic analysis of those afterglows
observed by XMM-Newton between January 2000 and March 2004. This dataset
includes GRB 011211 and GRB 030329. We have obtained spectra, light curves and
colors for these afterglows. In this paper we focus on the continuum spectral
and temporal behavior. We compare these values with the theoretical ones
expected from the fireball model. We derive constraints about the burst
environment (absorption, density profile) and put constraints on their beaming
angle.
