add a condition in an xml file showing all our products

I have an xml that i am using in my store to list all the products of our zen cart 1.3.9h store I need you to add a condition in this xml so if the value of a certain field of each product is (lets say) bigger than 3 then to exclude this product from showing in the xml file! I will provide you with a test server of mine to work. I am willing to give 20$ for this project - please bid only if you agree with this payment.