  We present a study of the decays B0 -> D0 K*0 and B0 -> barD0 K*0 with K*0 ->
K+pi-. The D0 and the barD0 mesons are reconstructed in the final states
f=K+pi-, K+pi-pi0, K+pi-pi+pi- and their charge conjugates. Using a sample of
465 million BBbar pairs collected with the Babar detector at the PEP-II
asymmetric-energy e+e- collider at SLAC, we measure the ratio
R_{ADS}=[Gamma(barB0 -> [f]_D barK*0)+Gamma(B0 -> [bar{f}]_D K*0)]/
[Gamma(barB0 -> [bar{f}]_D barK*0)+Gamma(B0 -> [f]_D K*0)] for the three final
states. We do not find significant evidence for a signal and set the following
limits at 95% probability: R_{ADS}(Kpi)<0.244, R_{ADS}(Kpipi0)<0.181 and
R_{ADS}(Kpipipi)<0.391. From the combination of these three results, we find
that the ratio rS between the b -> u and the b -> c amplitudes lies in the
range [0.07,0.41] at 95% probability.
