I am trying to construct a Word doc which can be emailed, filled in and
returned (Would that be an online form?) with some text boxes and some
yes/no check boxes. The text boxes work fine and while I have no trouble
adding the check boxes to the form but I can't figure out how User is
supposed to select them.

The only way I can place an X in one is to double click it in order to open
the "Check Box Form Field Options" dialog box and then select the
appropriate Default value. Surely this is not the normal way to check the
box, but then please tell me how else to do it?