Hi,

The best thing to do is to not add anything to the template or the header but to use an observer/notifier.

There is a load of information in the wiki....
http://www.zen-cart.com/wiki/index.p...Observer_Class
...including examples that show how to do things with the shopping cart.

Using an observer/notifier means that your contribution will touch less of the Zen Cart files and be easier to install and work better with upgrades.

Regards,
Christian.