As long as you'll have the points available (current or borrowed) at the time of the reservation, you can make another reservation thru MS.
If you have already borrowed your August, 2005 points for use in the 2004 Use Year (August 1, 2004 - July 31, 2005) - you can already make reservations for stays after August 1, 2005 by borrowing your 2006 points.
If you mean that you borowed (and already used) your August 2004 points and will get a new allotment of points on August 1, 2005- you could have already been using those points for reservations for Aug. 1, 2005-July 31, 2006 (and could have borrowed them for use between Aug.1, 2004 - July 31, 2005).
Enjoy!