My aunt and cousins live over there. Best shop on the island is Barnfield's Raging Isle in Haleiwa on the real North Shore. They have the goods, and when I was there last year they had some killer rentals available and were free with info on where to ride. Didn't actually make it to ride, that time, but next time I surely will. The ride to Kaena (spelling?) point looks fun, and as I understand it there are a ton of trails on Oahu.