Hiding fields based on selections in other fields

I'm using nodeprofile and pageroute to create a registration wizard. I'm having users enter a personal address on the first page and a shipping address on a subsequent page. The shipping address might be their own address or it might be a different address. If they want it sent to themselves (which they'd designate by choosing from a dropdown), I'd like those address fields hidden or grayed out. Otherwise, I'd like those fields required. Does anyone know how to do this?