i am planning to go in july or august of 2003! so NO! it is never too early to start planning!!!
as for making reservations this early that is another matter all together. it really depends on where you are staying and when they start taking reservations. if you are staying at a disney hotel i can tell you that you cant make ressies till April. i called 2 weeks ago and she said that is when i should call back, that they dont have 2003 rates yet.
happy planning......have you checked out the rewards board? if you have the extra time it is a great way to earn a few freebies. and you have plenty of time!