Answer:
   
   There is some disagreement about this. Most authorities believe that
   with the rebuilding of the temple would mean the reestablishment of
   animal sacrifices. Rav Kook suggests that animal sacrifices would not
   be brought back, he connects this to a suggestion that animals will be
   more humanlike in messianic times, and hence we will return to an Eden
   type vegetarian existence. The actual positions of the movement
   differ:
     * Orthodox. Orthodox Judaism calls for restoration of Temple and
       resumption of animal sacrifices.
     * Conservative. Conservative Judaism calls for the restoration of
       Temple, but does not ask for resumption of animal sacrifices. Most
       of the prayerbook passages relating to sacrifices are replaced
       with the Talmudic teaching that deeds of loving-kindness now atone
       for sin. In the Amidah the phrase na'ase ve'nakriv (we will
       present and sacrifice) is modified to read to asu ve'hikrivu (they
       presented and sacrificed), implying that animal sacrifices are a
       thing of the past. The petition to accept the "fire offerings of
       Israel" is removed.
     * Reform. Most of Reform Judaism calls neither for the resumption of
       sacrifices or the rebuilding of the temple, although some
       prayerbooks are moving towards calling for the latter.
       
   Note that we do not rebuild the Temple yet for a simple reason:
   ignorance. We do not know where on the Temple mount the altar or
   holy-of-holies are supposed to be. And places it a few feet off would
   violate the notion of only making offerings "in the place where I will
   show you." In fact, if we had the proper location down pat, we could
   rededicate the altar without building the Temple.