  Using data collected by the fixed target Fermilab experiment FOCUS, we
present several first measurements for the semileptonic decay $D^0 \to
\bar{K}^0\pi^-\mu^+\nu$. Using a model that includes a $\bar{K}^0 \pi^-$ S-wave
component, we measure the form factor ratios to be r_v= 1.706+-0.677+-0.342 and
r_2= 0.912+-0.370+-0.104 and the S-wave amplitude to be A=0.347+-0.222+-0.053
GeV^-1. Finally, we measure the vector semileptonic branching ratio
$\frac{\Gamma(D^0 \to K^{*}(892){-}\mu^+\nu)}{\Gamma(D^0 \to
\bar{K}^0\pi^-\pi^+)}= 0.337+-0.034+-0.013.
