  We present Swift and XMM observations of GRB 050326, detected by Swift-BAT.
The fluence was 7.7x10^-6 erg cm^-2 (20-150 keV), and its spectrum was hard,
with a power law photon index 1.25. The afterglow light curve did not show any
break nor flares between ~1 hr and ~6 d after the burst, and decayed with a
slope 1.70. The afterglow spectrum is well fitted by a power-law model,
suffering absorption both in the Milky Way and in the host galaxy. The
rest-frame Hydrogen column density is significant, N_H_z > 4x10^21 cm^-2, and
the redshift of the absorber is z > 1.5. There was good agreement between the
Swift-XRT and XMM results. By comparing the prompt and afterglow fluxes, we
found that an early break occurred before the XRT observation. The properties
of the GRB 050326 afterglow are well described by a spherical fireball
expanding in a uniform external medium, so a further steepening is expected at
later times. The lack of such a break constrains the jet angle to be >7 deg.
Using the redshift constraints provided by the X-ray analysis, we also
estimated that the beaming-corrected gamma-ray energy was >3x10^51 erg, at the
high end of GRB energies. Despite the brightness in X rays, only deep limits
could be placed by Swift-UVOT at optical/UV wavelengths. Thus, this GRB was
"truly dark", with the optical-to-X-ray spectrum violating the synchrotron
limit. The optical and X-ray observations are consistent either with an
absorbed event or with a high-redshift one. To obey the Ghirlanda relation, a
moderate/large redshift z>4.5 is required. (abridged)
