Use sections - they can be bound to any field, including the root, so no need to add a bunch of fields for your sections (not sure if this is a list or regular form). Then use conditional formatting on the section. I'd probably add a field for tracking status, no need to put it on the form. When the form is new, Status will be blank. Parts two and three can be hidden if status equals blank. When the user submits part one, you could set status to something like "Part one complete" and then you can hide part one when that is the status, etc.
Hilary Stoupa
