If you want to track the PHP-eSeller template driven shopping cart pages using Google Anaytic Javascript code then the best place for the code is in the file ‘footer.htm’ which is located in the /templates/ folder.
Just make sure that the Javascript code goes between the <patTemplate:tmpl name=”footer”> and </patTemplate:tmpl> and not outsite of those tags.
You should be able to test it by just looking at the source of the shopping cart web page when you display it in the browser. You should see the Javascript code somewhere near the bottom of the page.