  We present a kinematic model of the neutral-hydrogen in the spiral galaxy of
the lens system PKS1830-211, based on a Multi Element Radio-Linked
Interferometer (MERLIN) 1.4-GHz radio map and the integrated and redshifted
21-cm hydrogen absorption-line profile as measured with the Westerbork
Synthesis Radio Telescope (WSRT). Degeneracies in the models do not allow a
unique determination of the kinematic center and forthcoming deeper Hubble
Space Telescope observations with the Advanced Camera for Surveys (ACS) are
required to break this degeneracy. Even so, we measure the inclination of the
hydrogen disk: i=(17-32) deg., indicating a close-to face-on spiral galaxy. The
optical depth increases with radius over the extent of the Einstein ring,
suggesting HI depletion towards the lens center. The latter could be due to
star formation or conversion of HI in to molecular hydrogen because of a higher
metalicity/dust content in the galaxy center. The neutral hydrogen optical
depth gives N_HI= 2x10^21 cm^-2 at r=5.0 h_{70}^-1 kpc in the disk (T_s=100K),
comparable to local spiral galaxies. Our study shows that planned new radio
telescopes (i.e. ALMA, LOFAR and SKA) -- which will discover large numbers of
similar lens systems -- are powerful new tools to probe the internal structure,
kinematics and evolution of spiral galaxies in detail to z>=1, as well as their
neutral-hydrogen (and molecular) content, thereby complementing studies of HI
emission from spirals at z<=1 and damped Ly-alpha systems to z>>1.
