Rajah,
I may be wrong, but I THINK only the Big Island has black sand beaches, because it is the "newest" island and still has traces of recent lava flow. Kauai is the oldest island, so I would think that they would be the least likely to have black sand beaches. However, it is quite possible that I could be wrong, even though I've lived on Oahu all my life, I've spent more time visiting other states than I have the other islands! I'll see if I can find out anything more about it.
FOJMO,
I'm not sure about where surf lessons are offered, but I'm sure if you asked at the hotel, or even just walked along Waikiki Beach, you should be able to find someone. We know people from Florida who were visiting a couple weeks ago, and they mentioned something about surf lessons. Waikiki is very popular for surfing, closer to shore the waves are small enough for beginners, but further out is where the more experienced surfers like to go. Sorry I can't offer anything more specific, but I know there is somewhere next to the Moana Surfrider which I think offers lessons -- if I'm not mistaken, the guy who runs it is a classmate of mine (a family business, so it's been in operation for years).
And whoever mentioned the Kahala Mandarin, yes, if you can afford it, it is a beatiful place! The beach there is probably a lot less crowded than Waikiki, yet if you have a car, it is still very close to Waikiki and not as secluded as the resorts on the north and west shore.
