  We combine lensing, stellar kinematic and mass-to-light ratio constraints to
build a two-component (luminous plus dark) mass model of the early-type lens
galaxy in PG1115+080. We find a total mass density profile steeper than r^-2,
effectively rho r^-gamma' with gamma'=2.35+-0.1+-0.05 (random + systematic).
The stellar mass fraction is f*=0.67(+0.20/-0.25)+-0.03 inside the Einstein
Radius (R_E 1.2 effective radii). The dynamical mass model breaks the
degeneracies in the mass profile of the lens galaxy and allows us to obtain a
value of the Hubble Constant that is no longer dominated by systematic errors:
H_0=59(+12/-7)+-3 km/s/Mpc (68 percent C.L.; Omega_m=0.3, Omega_L=0.7). The
offset of PG1115+080 from the Fundamental Plane might indicate deviations from
homology of the mass profile of some early-type galaxies.
