The 2010 rates should be out around August, 2009. I believe you can book a year ahead of time (if I am wrong somebody will correct me) but your rate will be adjusted when the 2010 rates are published.
I believe I heard that you can book your trip 499 days in advance. Or at least that is what I read from a thread that was created on the DIS in June of 2008.
It's just they most likely won't have the prices available until August of 2009.
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