The semileptonic decay B->pi is studied starting from a simple quark model
and taking into account the effect of the B* resonance. A novel, multiply
subtracted, Omn\`es dispersion relation has been implemented to extend the
predictions of the quark model to all physical q^2 values. We find
|V_{ub}|=0.0034 +/- 0.0003(exp.)+/- 0.0007(theory), in good agreement with
experiment.Comment: Three pages, two figures. To appear in the proceedings of Quark
Confinament and Hadron Spectrum VII. Azores, September 200
