No, you don't have to (and can't) pay your 2010 MF now. The only MF requirement to reserve your 2010 week and request an exchange is that you not be delinquent on any MFs. So if you pay the fees that are due this month timely, you will have no problems making your reservation.
As stated, you can reserve your 2010 week 12 months in advance, assuming you own a single Marriott week. Pick an early week to reserve and deposit so that you can request your summer 2009 week in exchange. However, summer is a popular time at Barony, so trading back in for this summer at this late date won't be easy. Also, your Platinum season doesn’t start until June, so you won’t be able to reserve your 2010 summer week until then, giving yourself almost no time for a successful exchange for this summer.
A better plan, if you can wait, would be to forego your use this summer and try to make your idea work in 2010. Deposit your 2009 week with II now and immediately make your exchange request for the 2010 week you want. That way, you'll be in line for an exchange when many owners reserve and deposit their summer 2010 weeks this coming summer. You'll likely get the exchange you want and you can reserve your own 2010 week this summer, thus getting the two weeks you want - in 2010, not 2009.