hi,
I don't know what your meant by XML, but you can use javascript to control your form as following:
Try to group your section in a subform. , initialise all subform to be invisble using javascript in the Form:Open event.
ie.
F.P1.SubForm1.presence = "hidden";
Then depend on the your selection, which you can enable the form as
F.P1.SubForm1.presence = "visible";