How to set value for PO Approval form checkbox /

Hi,

           I want to set the value for a check box item (EMAIL_CHECK) on PO approval form(POXPOEPO) Transmission Methods section. This is a check box item and at run time it becomes a radio button. I tried following, both didn't work.

                  copy('N','PO_APPROVE.RADIO_PRINT_FAX_EMAIL.EMAIL_CHECK');

copy('N','PO_APPROVE..EMAIL_CHECK');

                   Please help.

Thanks