Sorry about the lack of response - have been out of town
Anyways, I am using version 1.7 - having just dug around a bit I've discovered that it's probably something in the theme I am using that's causing this, as the archive IS indeed shown in reverse chronological order when using the the simple theme.
It would seem that the tag <THUMBNAILS_WHOLE_PAGED> is the cause of this - I do have the addon installed but it would appear this is showing the thumbnails in the actual chronological order - any way to go around this?