When Purim falls on Mosa’eh Shabbat (as it does this year, 5774), one must ensure not to make any preparations for Purim on Shabbat. Thus, for example, even in places with an Erub, one may not bring the Megila to the synagogue to prepare for the Megila reading. Similarly, one may not prepare Mishloah Manot packages on Shabbat, and the Gabbai may not prepare the Torah scrolls on Shabbat for the Purim reading. It is permissible, however, to review the Megila on Shabbat, even if one is preparing to read it that night, because the reviewing itself constitutes a Misva, as it involves Torah learning. Even in such a case, one should preferably avoid stating outright that he is reviewing the Megila in preparation for the reading on Purim.
It should be noted that a Megila is not considered Mukseh, and thus one may read from an actual Megila on Shabbat.
It is customary to delay the Arbit service on Mosa’eh Shabbat to allow people the time they need to get to the synagogue. After the Amida prayer in Arbit, the Hazzan recites half-Kaddish, which is followed by Shuba Hashem and Yosheb Be’seter, until but not including Ve’ata Kadosh. At that point, the Megila is read, and Ve’ata Kadosh is read after the reading. According to some opinions, the Beracha of "Boreh Me’oreh Ha’esh" is recited over a flame before the Megila reading. (This is the view of the Hida, in Birkeh Yosef, as cited by the Kaf Ha’haim.) The rest of Habdala, however, according to all opinions, is delayed until after Megila reading, except if one is reading the Megila at home, in which case he should recite Habdala before reading the Megila. Even in such a case, though, he and his family may not eat until after the Megila reading. Those who recited or heard the Beracha over the flame in the synagogue may not recite it again later at home, even if they are reciting Habdala for their wives and children. In such a case, the wife should recite the Beracha herself.
Although the obligation of Se’udat Purim (the Purim feast) applies only on Purim day, it is proper to have a meal on the night of Purim in honor of the holiday. This is especially true when Purim falls on Mosa’eh Shabbat, when one in any event is required to eat a Melaveh Malka meal. Therefore, one must exercise particular caution during Se’uda Shelishit to eat moderately so he will be able to eat a Se’uda that night.
