Annual dues apply on an annual calendar basis. Regardless of when your allotment of points comes in a year, you can still be assessed dues for the entire calendar year (or partial year if it opens during the year). Thus, the fact that you have a Sep use year does not itself prevent you from having to pay any dues applicable to 2009 once the resort is open.
However, which dues you will be assessed for 2009 depends on what your contract documents say. You should check it because I cannot remember what the usual wording is right now. If it says dues will be assessed starting Sep 1, then you don't pay for Aug. However, it may say something like dues will be assessed beginning when your unit becomes available for occupancy, in which case that would be Aug. Or it might even say you will begin to pay dues Sep 1 or, if later, the date your unit becomes available for occupancy in which case you would not pay Aug. I am drawing a total blank of what is usually said right now but there should be something in your documents.