Holding Account points can only be used for reservations within 60 days when you call. In addition, they cannot be banked and will expire at the end of the current Use Year.
If you have an August Use Year, the points would need to be used by July 31, 2011 and cannot be used for a reservation after that date.
If you had an existing reservation prior to August 1, it's possible they could be used (within 60 days of arrival) providing there was availability at the resort - otherwise it would likely involve a cancellation and rebooking if there is a waitlist for those dates. MS has not always been consistent with how they handle that, so it can't hurt to ask. Regardless, Holding Account points can't be extended into another Use Year so your August trip won't work for those points.