@doreendotan: HaNachash is HaMashiach.
Yeranen Yaakov: The Gr"a explains that the snake is a hint to Mashiah, who is a descendant of Yishai (King David's father), who is called a "snake" (see Shemuel Bet 17 and Shabbat 55b). Similarly, as is known, נחש is the same gematria as משיח (both are 358 - see Adir Bamarom by the Ramha"l, p. 339). The gestation period of a snake symbolizes the period of numerous and terrible troubles which are said to come before Mashiah, and which are named by Haza"l 'The birthpangs of Mashiah,' since the verse allegorizes it to birth pangs that precede the birth of a child (Yeshaya 26:18, Yirmiya 30:6; see Sanhedrin 95b and Ketubot 111a).
