You need to be careful here, I think.
I believe that if you only edit the template file, it won't work properly, and in fact you only solve half the problem. While it looks like it works, when you place an order, is it going back to the page, but appearing to place the order?
You need to edit:
payment/payment_offline.php
and look for line 53:
it looks something like this, and explains why it shouldn't work if you ignore this file:
Code:
if(empty($Company_name) || empty($Name_of_purchaser) || empty($Position)) {
that is the correct code for removing the PO no only. Remove the others as you need.
Also, be careful you are not getting a javascript error when you submit the order.
If you remove only PO no you need to renumber the array, so it starts at 0.
Hope this helps you or anyone else trying to do this.
(It's too hot for quilts by the way!!!)