There's a Dragon Magazien article that updates OA to 3.5e. Can't remember which issue, though.
Also, do NOT use the Complete Warrior samurai. It sucks, the OA one is a lot better. The CW samurai is a crappy class based off of Miyamoto Musashi, the samurai kensei who invented "Two Heavens as One" technique known as niten-ichi and half based off of the Intimidate skill. It's useless because Intimidate doesn't work on everything, can be defeated easily with immunity to fear, and the niten-ichi abilities and other abilities are only based on a katana and wakizashi...better carry around several katanas and wakizashis for whenever they're lost, stolen, or sundered.