This is the thread I think you're referring to:
http://www.pixelpost.org/forum/showthread.php?p=56700#post56700
In your PP admin, go to Options>>General and scroll down to the bottom of the page. Under
IMAGE DISPLAY ORDER, make sure that the first option is set to "date and time of entry" and the 2nd option is set to "descending" to display the latest image first in your archive.