Bring water and sugar to a boil in a medium saucepan, stirring often; reduce heat, and simmer 5 minutes, stirring occasionally. Cool; cover and chill. Process peach slices and lemon juice in a blender until smooth, stopping once to scrape down sides. Combine sugar mixture, peach mixture, orange juice, and almond extract; pour into freezer container of a 4-quart hand-turned or electric freezer. Freeze according to manufacturer's instructions. Pack freezer with additional ice and rock salt, and let stand 1 hour before serving.