Shipping method determined by a custom checkout filed

Hi,

Does anyone has any idea on how could I achieve this?

I have a custom field in the checkout page, allowing the customer to choose a packaging option. I need to determine the shipping method based in this selection, because there is only one shipping option for each packaging selection.

Eg. If the customer chooses to have a gift wrapping, only delivery company A is available – shipping method A with cost A. If the customer chooses to have a standard wrapping, than only delivery company B is available – shipping method B with cost B.

Many thanks