I have what is essentially a shopping cart that needs to have two separate checkout options. The first of which takes the user away from the site, but form data must be post
If I understand correctly, you have 2 submit buttons on the same page and both of them have the same form if that is so, this should do the trick.
if(isset($_POST['name1'])) { //do stuff } if(isset($_POST['name2'])) { //do other stuff }