  We present a study of the decays B0->D_s(*)+D*-, using 20.8 fb-1 of e+e-
annihilation data recorded with the BABAR detector. The analysis is conducted
with a partial reconstruction technique, in which only the D_s(*)+ and the soft
pion from the D*- decay are reconstructed. We measure the branching fractions
BR(B0->D_s+D*-) = (1.03 +/- 0.14 +/- 0.13 +/- 0.26)% and BR(B0->D_s*+D*-) =
(1.97 +/- 0.15 +/- 0.30 +/- 0.49)%, where the first error is statistical, the
second is systematic, and the third is the error due to the D_s+->phi pi+
branching fraction uncertainty. From the B0->D_s*+D*- angular distributions, we
measure the fraction of longitudinal polarization Gamma_L/Gamma = (51.9 +/- 5.0
+/- 2.8)%, which is consistent with theoretical predictions based on
factorization.
