You can go ahead now and book the rooms for 2009. We are going Easter/Spring 2009 and I wanted to make sure I had a reservation at AKL. They will price you the highest room rate for 2008 and you have to put down one nights deposit. When the packages are released later this year you can call and they will adjust everything with the correct pricing. I think they go ahead and adjust the room only rate even if you don't call.
The cast member I talked with told me to check in once the 2009 rates were released periodically to see if there were any discounts. He said it was no problem to adjust the current reservation if there was. I hope he was correct. I would call Disney and just ask. I have always had good service with them.