Seems your use year is Dec? Am I correct? If so, you would bank your 08 points by July 09 and then as long as you have enough points by the time your trip comes you can book your cruise whenever (jan 09) if that is first available time to book it (I am also new to this & I don't know if you have to be so many months out to do cruises) Banking 08 points will allow those points to "carry over" and then you would obtain your 09 points (in Dec??) if your trip is in June 2010 the only thing you would have to worry about is if for any reason you would have to cancel- your 2008 points would be lost if not used and you would have to use or bank 09 points quickly as not to lose them as well- As long as you don't think that you'd have to worry about cancellation you should be fine-
Someone else could probably give you a bit more detailed info though- We are also new & I have never taken a cruise- We are also staying on Developer points next year...