[Christofer]

no basically it's not that exactly the problem. The problem is that i asked QT to make a code for me. The code i wanted was :
I have a product hidden extra field for products that i ship with e-mail, when it's "Y" an icon appears on product description and informs customers.

Also for those products i check the "Free shipping" to hide the shipping options. So i asked the QT to give me a code that will hide the COD payment method when the extra field is "Y".

They gave me a code that didn't work, and after a few messages, they told me that the code is correct, but doesn't work because i use One page checkout, coz the one page checkout processes the variable $display_cod wrong..

Anyway, in the last message from QT to prove me the thing about variable, they told me that the one page checkout displays the COD payment method even if the product is checked with free shipping..