Thanks for the extra information around your process. I think we can help you but we could also use a little more information of how you have your InfoPath form set up. For instance, if you have a submit button, what is it submitting to and how are you pushing data into your database. You may have to add some logic that will tell if you are going just a project insert versus a project and a plant insert.
Jason
http://www.k2distillery.com/