I called yesterday and asked that same question, for May 2009. I was told that you can book now at the 2008 rates, and then they will adjust the price when the 2009 prices come out "sometime in August." The CM I spoke with said they dont even have the "seasons" for 2009 listed yet, and that the "regular", "value" and "peak" room rates could of course be changing for 2009. Just something to look out for if you are worried about pricing.
But you can reserve the rooms now, I was told.
Good luck with your planning!