  We have estimated the bulge-to-total ($B/T$) light ratios in the $K_s$-band
for a sample of 24 S0, S0/a and Sa galaxies by applying a 2-dimensional
multicomponent decomposition method. For the disk an exponential function is
used, the bulges are fitted by a S\'ersic's $R^{1/n}$ function and the bars and
ovals are described either by a S\'ersic or a Ferrers function. In order to
avoid non-physical solutions, preliminary characterization of the structural
components is made by inspecting the radial profiles of the orientation
parameters and the low azimuthal wavenumber Fourier amplitudes and phases. In
order to identify also the inner structures, unsharp masks were created:
previously undetected inner spiral arms were found in NGC 1415 and marginally
in NGC 3941. Most importantly, we found that S0s have a mean $<B/T>_K$-ratio of
0.24 $\pm$ 0.11, which is significantly smaller than the mean $<B/T>_R$ = 0.6
generally reported in the literature. Also, the surface brightness profiles of
the bulges in S0s were found to be more exponential-like than generally
assumed, the mean shape parameter of the bulge being $<n>$ = 2.1 $\pm$ 0.7. We
did not find examples of barred S0s lacking the disk component, but we found
some galaxies (NGC 718, NGC 1452, NGC 4608) having a non-exponential disk in
the bar region. To our knowledge our study is the first attempt to apply a
multicomponent decomposition method for a moderately sized sample of early-type
disk galaxies
