  In this paper we present new measurements of the gas kinematics in M33 using
the CO J=1-0 line. The resulting rotational velocities complement previous
21-cm line data for a very accurate and extended rotation curve. The implied
dark matter mass, within the total gaseous extent, is a factor 5 higher than
the visible baryonic mass. Dark matter density profiles with an inner cusp as
steep as R^{-1}, are compatible with M33 data. The dark matter concentrations
required for fitting the M33 rotation curve are very low but marginally
consistent with halos forming in a standard Cold Dark Matter cosmology. The M33
virialized dark halo is at least 50 times more massive than the visible baryons
and its size is comparable with the M33-M31 separation. Inner cusps as steep as
R^{-1.5} are ruled out, while halo models with a large size core of constant
density are consistent with the M33 data. A central spheroid of stars is needed
and we evaluate its dynamical mass range. Using accurate rotational velocity
gradients and the azimuthally averaged baryonic surface densities, we show that
a disk instability can regulate the star formation activity in M33. Considering
the gaseous surface density alone, the predicted outer star formation threshold
radius is consistent with the observed drop of the H-alpha surface brightness
if a shear rate criterion is used. The classical Toomre criterion predicts
correctly the size of the unstable region only when the stellar or dark halo
gravity, derived in this paper, is added to that of the gaseous disk.
