Yes, order is being stored correctly in the database ("... the order and order details entries are posted correctly ...").
Re: "is the transaction showing under Authorize.net"
Authorize.net is in test mode:
"ACCOUNT IS IN TEST MODE - REAL TRANSACTIONS WILL NOT BE PROCESSED"
I do not have any way to know or prove that they are reaching authorize.net correctly (it does not seem to store "test" transactions) however I believe it is working correctly since (as I mentioned before) we are getting a valid test confirmation email FROM authorize.net with all the corect information. So apparently that means authorize.net is receiving everything from our shopping cart that it is supposed to be receiving.
If you can give me instructions on how to provide you with better information than that, please do. All this is new to me.
In the mean time - we're stil anxiously waiting your report on what might be wrong with the current page. We suspect it must be a problem with the confirm.php page but we don't know for sure.