MS Word 2003 document protection not allowing forms to be filled in.

I haven't created forms in Word much in the past and I'm trying to create a Fax template in Word 2003 that contains MACROBUTTON text fields. The idea is so that all text in the document is locked (protected) and only the fields can be edited. I presume this is done by going to Tools > Protect Document then checking the allow only filling in forms option. Once this is done it prevents text being edited but it also prevents the fields from being edited also.

I have used the MACROBUTTON method instead of the form text field because the sample Microsoft templates in Word use this method so I would expect it to be compatible with these fields.

Any ideas if this should work? I followed a few tutorials illustrating this as the method.