NA60 is an experiment at the CERN-SPS devoted to the study of dimuon production in heavy-ion and proton-nucleus collisions. The main topics under study are low mass vector meson production, J/\(\psi\) production and suppression, and the sources of the dimuon continuum in the mass range 1.2-2.7 GeV/c2. In 2003, NA60 collected \(\sim 230\) million dimuon events from Indium-Indium collisions. We present preliminary results of the analysis of this data sample in view of measuring the open charm contribution to the dimuon spectrum. Although we are still working on the final background subtraction procedure, we can already demonstrate that the detector performance is good enough to allow the separation of prompt dimuons from muon pairs originating in distant D \(\overline{\rm D}\) decays.