We consider the scalar form factor in $\tau \to K\pi \nu_\tau$
decays. It receives contributions both from the scalar resonance
$K_0^*(1430)$ and from the scalar projection of off-shell vector resonances.
We construct a model for the hadronic current which includes the vector
resonances $K^*(892)$ and $K^*(1410)$ and the scalar resonance
$K_0^*(1430)$. The parameters of the model are fixed
by matching to the $O(p^4)$ predictions of chiral perturbation theory.
Suitable angular correlations of the $K\pi$ system
allow for a model independent separation of the vector and scalar
form factor. Numerical results for the relevant
structure functions are presented.