Unless I am misunderstanding you, I think what you are concerned about is waiting till 1 year before weeks 51 and 52, since if you don't get them, you now are a few weeks to a few months away from the rest of your platinum season (wince weeks 1-17 are right around the corner). If I understand your question correctly:
-for December 2007- at this point, you might as well just wait till one year in advance and try to get week 51. Make sure to call at 9AM Thursday morning (exactly one year ahead of the first check-in day for the week). If you can't get week 51, then try again for week 52. Otherwise, at that point, you might as well book the best week you can in Jan.- April
-for your 2008 reservation- what I would do is pick a week you would otherwise be happy with during weeks 1-17, and book that 1 year ahead. Then, come December of 2007, try to get week 51 or 52 if you prefer that. You can change a reservation for I believe a $29 change fee- well woth it to secure a good week if you strike out for the holidays