Thanks for your help so far.
Thanks for your help Eric.
I'm happy this will be feasible.
I'll be continuing with help requests though as this is the first time I'm trying something like this.
I found the code in the two files confirm.php and pp_confirm.php,
I'll try to study the behaviour and figure out how I can modify it for Australia Post.
If you have any more pointers (what does what etc) please post them here.
Again thanks for your help