If you want to go in January, particularly around the Marathon Weekend (01/11-01/13) I would reccomend calling CRO and making a room only reservation now. You will have to book at this year's rates so they will probably go up once the 2008 rates are released (usually its just $10-$20 per night more depending on the hotel) and if you want a package you will have to switch your stay to a package reservation, but you are guaranteed the room type and resort you want.
If you know what you want to book now, I would reccomend calling because, at least around that weekend, certain room types are already completely booked. The only thing it costs is a 100% refundable first night's deposit and the reservation itself is cancellable with no penalties up to 5 days before your arrival date bceause it is room-only. If you are still up in the air about what you want, I might hold off, but if you have a one or two particular room types/resorts in mind, you should probably call now.