We study the propagation and attenuation of zero sound and first sound in thin, arbitrarily polarized Fermi-liquid films. Following Khalatnikov and Abrikosov, we solve Landau's linearized kinetic equation in the relaxation-time approximation for a complex speed of sound. Analytic solutions are obtained in the hydrodynamic and ballistic limits for arbitrary polarization. By solving the collision integral in two dimensions, we find the well-known result that quasiparticle-quasiparticle collisions contribute to the collision frequencies 1/τ σ , with a low-temperature term proportional to T 2 ln (T F σ /T ), where σ = ↑, ↓ is the spin state. If the films are adsorbed to a dynamic substrate, we find additional possible contributions to the collision frequency that come from quasiparticle-phonon interactions. We show, however, that for 3 He thin films, the mismatch between possible maximum values of the Fermi velocity and the substrate speed of sound freezes this contribution out at usual experimental temperatures. Thus, we can conclude that zero sound propagates at absolute zero in this type of adsorbed Fermi-liquid film. By utilizing previous results for the Landau parameters of an arbitrarily polarized 3 He film, we compute numerical solutions for the sound speeds and attenuation in the hydrodynamic and ballistic regimes, thereby studying the transition from first sound to zero sound as a function of temperature.