We present high angular resolution submillimeter continuum images and molecular line spectra obtained with the Submillimeter Array toward two massive cores that lie within infrared dark clouds (IRDCs), one actively star-forming (G034.43+00.24 MM1) and the other more quiescent (G028.53-00.25 MM1). The high angular resolution submillimeter continuum image of G034.43+00.24 MM1 reveals a compact (～0.03 pc) and massive (～29 M_☉) structure, while the molecular line spectrum shows emission from numerous complex molecules. Such a rich molecular line spectrum from a compact region indicates that G034.43+00.24 MM1 contains a hot molecular core, an early stage in the formation of a high-mass protostar. Moreover, the velocity structure of its ~(13)CO (3-2) emission indicates that this B0 protostar may be surrounded by a rotating circumstellar envelope. In contrast, the submillimeter continuum image of G028.53-00.25 MM1 reveals three compact (～0.06 pc), massive (9-21 M_☉) condensations, but there are no lines detected in its spectrum. We suggest that the core G028.53-00.25 MM1 is in a very early stage in the high-mass star formation process; its size and mass are sufficient to form at least one high-mass star, yet it shows no signs of localized heating. Because the combination of high-velocity line wings with a large IR-to-millimeter bolometric luminosity (～ 10~2 L_☉) indicates that this core has already begun to form accreting protostars, we speculate that the condensations may be in the early phase of accretion and may eventually become high-mass protostars. Therefore, we have found the possible existence of two high-mass star-forming cores: one in a very early phase of star formation and one in the later hot-core phase. Together, the properties of these two cores support the idea that the earliest stages of high-mass star formation occur within IRDCs.
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