Physics with tau's in the final states at CMS

On the eve of LHC start-up, the main opportunities offered to CMS to discover and ultimately study new physics with tau's in the final states are presented. From the discovery of the Higgs boson in the Standard Model, of its extension in the MSSM or in non-SUSY alternatives to the measurement of SUSY mass spectrum in $q~ \to q\xi~^{0}_{2} \to q\tau \tau ~$ cascade decays, this talk reviews the most recent analyses developed in the CMS collaboration for the low luminosity $2 · 10^{33}cm^{-2}s^{-1}$ running phase of the LHC.