  The accurate determination of Saturn's gravitational coefficients by Cassini
could provide tighter constrains on Saturn's internal structure. Also,
occultation measurements provide important information on the planetary shape
which is often not considered in structure models. In this paper we explore how
wind velocities and internal rotation affect the planetary shape and the
constraints on Saturn's interior. We show that within the geodetic approach
(Lindal et al., 1985, ApJ, 90, 1136) the derived physical shape is insensitive
to the assumed deep rotation. Saturn's re-derived equatorial and polar radii at
100 mbar are found to be 54,445 $\pm$10 km and 60,365$\pm$10 km, respectively.
To determine Saturn's interior we use {\it 1 D} three-layer hydrostatic
structure models, and present two approaches to include the constraints on the
shape. These approaches, however, result in only small differences in Saturn's
derived composition. The uncertainty in Saturn's rotation period is more
significant: with Voyager's 10h39mns period, the derived mass of heavy elements
in the envelope is 0-7 M$_{\oplus}$. With a rotation period of 10h32mns, this
value becomes $<4$ $M_{\oplus}$, below the minimum mass inferred from
spectroscopic measurements. Saturn's core mass is found to depend strongly on
the pressure at which helium phase separation occurs, and is estimated to be
5-20 M$_{\oplus}$. Lower core masses are possible if the separation occurs
deeper than 4 Mbars. We suggest that the analysis of Cassini's radio
occultation measurements is crucial to test shape models and could lead to
constraints on Saturn's rotation profile and departures from hydrostatic
equilibrium.
