Vibrationally inelastic electron transport through a molecular bridge that is connected to two leads is investigated. Employing methods from electron-molecule scattering theory, the transmittance through the molecular bridge can be evaluated numerically exactly. Performance of various approximations is tested. The methods are applied to two models. In the first model we treat one harmonic mode coupled to tunelling electron and to dissipative bath. The second model is designed to mimic anharmonic torsional vibrations of biphenyl molecule.