Previous poster is correct. For the last two years, the rates have come out on or about August 15th.
If you have your heart set on a specific resort, you can go ahead and book a room only reservation. You will be charged 2008 rates and when the 2009 rates come out, your total will be adjusted to reflect the 2009 rates. If this is the route you take, you will be required to pay a deposit equal to your first night's stay.
If you decide to change the room only reservation to a package, you can call Disney reservations. Before you call, you need to know which package you want so that the booking will go quickly. Tell the castmember that you have a room only reservation and you would like to now book a package.
They will actually have to cancel the room only reservation and you will be refunded your room only deposit. They can not transfer the deposit to the package reservation. Depending on how you paid for the room only reservation, you could have your deposit refunded anywhere from 5 days (which is what happened to me) to over a month (which I have read about on these boards).
When you book the package, you will be required to pay a $200.00 deposit within fourteen days fron the date you book the package. From that point, you can start making payments on your package as often as you wish in any amount you wish. The only requirement is that you have the package paid off 45 days prior to arrival and make a minimum payment of $20.00. I love this because it feels like you have your vacation on layaway.
Hope this information helps.