Thanks for your comments Frank.

My original post was not completely clear about the checkout steps, and they have different names in different areas of the screen (I am using cherry zen, and checkout without account, so that may have caused the differences), so I will try to clarify:
Step 4/5
Page: index.php?main_page=checkout_confirmation
Page title: Order Review

This is where the default setup shows the bank account details, but from what I have read, the order number has not been created yet, until someone clicks "confirm order" and moves to:
Step 5/5
index.php?main_page=checkout_success
Page title: Thank You! We Appreciate your Business!/Checkout Successful
At this point you actually have an order.

I have been doing some experimenting and have some answers, but none of them are good.

Code:
define('MODULE_PAYMENT_DIRBANKNZ_TEXT_EMAIL_FOOTER', 
  "Please use the following details to transfer your total order value:\n\n" .
  "\nAccount No.:   " . MODULE_PAYMENT_DIRBANKNZ_ACCNUM .
//  "\nRouting Number:" . MODULE_PAYMENT_DIRBANKNZ_ROUTING . 
  "\nAccount Name:  " . MODULE_PAYMENT_DIRBANKNZ_ACCNAM . 
  "\nBank Name:     " . MODULE_PAYMENT_DIRBANKNZ_BANKNAM .
  "\nReference:     " . $zv_orders_id .                       
  "\n\nThanks for your order which will ship immediately once we receive payment in the above account.\n");
Doesn't add the order number to the email. I guess that the variable $zv_orders_id is not available to that page. Adding "global $zv_orders_id" doesn't work either.

I could just tell the customer to look it up, but that is a hassle for them and I think the less effort for customers, the more $ for me.

As far as the web pages go, I am thinking something along this line:
Code:
 define('MODULE_PAYMENT_DIRBANKNZ_TEXT_DESCRIPTION', 
  '<BR>You have chosen to pay by direct deposit, our bank account details will be displayed on the next screen when you confirm your order.');
And then modify includes/templates/MY_TEMPLATE/templates/tpl_checkout_success_default.php
to check to see if the payment method was DIRBANKNZ and if so display the account details.

Unfortunately at this point I am stuck. I can see several people wanting to do similar things in the forums, but no notes about anyone actually succeeding. I can see arrays with the information I need, but any attempts at getting the information end up with error messages along the lines of "you obviously know nothing about php, arrays or classes, here is a banana, now go away" Or at least they seem that way to me

Any pointers would be appreciated.

Pat