In a small saucepan, cover the dried cranberries and blueberries with boiling water and let stand until softened, about 5 minutes. Drain well.
Heat the oil in the same saucepan. Add the curry and garlic and cook over low heat for 1 minute; discard the garlic. Add the honey, salt and cayenne, then whisk in the orange juice. Stir in the dried fruits and bring to a simmer. In a large bowl, toss the spinach with the hot dressing and serve at once.