If you are using Forms 2.0, on the right hand side select the field type 'Checkbox' and then customize the values to be just 'Yes' when it is checked. When its unchecked it will automatically be no.
If you are using Forms 2.0, on the right hand side select the field type 'Checkbox' and then customize the values to be just 'Yes' when it is checked. When its unchecked it will automatically be no.