  Charged current charm and D meson production is studied in detail as a means
of determining the unpolarized and polarized strange sea densities at HERA. All
analyses are performed in next-to-leading order QCD, including a calculation of
the so far unknown spin-dependent MSbar coefficient functions up to O(alpha_s).
It is shown that a decent measurement is possible in the unpolarized case,
provided a sufficient luminosity can be reached in the future, while for
longitudinally polarized beams it appears to be extremely challenging due to
limitations imposed on the expected statistical accuracy by the charm detection
efficiency.
