I am trying to implement a quadratic model via Sorkep subroutine, but something is not working right, the influence of the nonlinear terms is practically '0'.. anybody ever tried somethig similar??

There's a version of sorkep with the non-linear model available from CD. Ask your local support office for it.

Thank you very much richard, I will try again..I am in japan and i have asked them but they said they don't have any... If by chance you can obtain it from your local CD I would be gratefull to you..