  We explore the possible impact of galactic and extragalactic foregrounds on
measurements of the cosmic microwave background (CMB). We find that, given our
present understanding of the foregrounds, they are unlikely to qualitatively
affect the ability of the MAP and Planck satellites to determine the angular
power spectrum of the CMB, the key statistic for constraining cosmological
parameters. Sufficiently far from the galactic plane, the only foregrounds that
will affect power spectrum determination with any significance are the
extragalactic ones. For MAP we find the most troublesome foregrounds are radio
point sources and the thermal Sunyaev-Zeldovich (SZ) effect. For Planck they
are these same radio point sources and the Far Infrared Background. Prior
knowledge of the statistics of the SZ component (either via theoretical
calculation, or higher frequency observations of just a few percent of the sky,
such as will be done by balloon-borne experiments) may significantly improve
MAP's determination of the CMB power spectrum. We also explore the foreground
impact on MAP and Planck polarization power spectrum measurements.
