This popular dish takes time to prepare. However, you can make the sauce in advance and keep it in the freezer or refrigerator. For an authentic dish, don't take shortcuts and don't leave out any of the ingredients-particularly the Pad Thai sauce that gives the final dish its rich, amber color and succulent taste. Select the rice stick noodles marked "M" for medium; the thinner and the wider ones are used for other noodle dishes. Salted or preserved radish is sold in cellophane packets at Asian markets and, after opening, lasts almost indefinitely in the refrigerator. Be sure to have all the ingredients within reach because you have to work fast and be at the stove throughout the cooking time. With one bite of this Pad Thai, you will discover noodle heaven.