I am not the worlds greatest coder but I can usually hack together bits and pieces as needed, but in the hopes of saving myself a medium lifespan's worth of time I wonder if anyone can point me in the general direction of where I can hook in some code..

Basically what I need to do is check through the order after it has been placed and paid for for a specific product, if that product is included in the order I need to perform some calculations on attributes and then email the results to myself.

The email forms a check list which I use to make the product and check off various quality issues during the manufacture.

Getting the info from the database, extracting the bits I need, forming the email and sending it are not problems I need help with, that is all pretty much already done on my existing site.

What I need to know is where I can intercept the program flow and slip my hack in, it needs to be done after the order has been made and paid for. At the moment I use Paypal IPN and do everything in the IPN validation script on my non zencart site.

If anyone has any ideas I would be very grateful ;)