Prepare the Hollandaise sauce, and keep it warm. Mix the water with the vinegar (which will help the egg whites set quickly) and put it with the salt in a wide, shallow saucepan. Bring water to boil, then reduce heat to gentle simmer. One at a time, break each egg into a separate small dish or bowl; then, holding the bowl very near the surface of the water, gently slip in the egg. Add more eggs to the pan, taking care not to crowd them. Continue simmering until whites are firmly set and yolks are covered with slightly opaque film, about 3 minutes. Then use a slotted spoon carefully to remove each egg to a folded kitchen towel to drain. With small kitchen knife, carefully trim any ragged edges from whites. While the eggs are poaching, melt half the butter in large skillet over moderate to low heat, and saute the crab meat until heated through. Split and toast the English muffins and spread their cut sides with remaining butter. Place two muffin halves on each serving plate. Top each half with some crab meat and then a poached egg. Spoon or pour enough Hollandaise over each egg to cover it and spread down the side of the muffin onto the plate. If you wish, garnish with a dusting of paprika and half an orange slice. Makes 4 servings. ORANGE HOLLANDAISE SAUCE: In a small saucepan, melt butter over low heat until it's all liquid. place remaining ingredients in a food processor or blender and process until smoothly blended. With the machine running, pour in the melted butter in a slow, steady stream until it is completely mixed in and the sauce is thick. transfer sauce to small metal or glass bowl, and set it inside a larger bowl or 1)an of hot water to keep it warm. Makes about 1 1/4 cups. "Breakfast & Brunch Book" (HPBooks, $19.95), from the Hayward Daily Review, 11/9/92.