Cut pears in half lengthwise. Put sugar and water into a saucepan and bring to a boil, then reduce heat and simmer 5 minutes. Stir in vanilla, add pears, and simmer another 15 minutes, until pears are tender. Allow pears to cool in the syrup. To serve, place one scoop of ice cream onto each of 4 chilled plates. Arrange 2 pear halves on either side of ice cream, then spoon chocolate sauce over all and top with almonds.