Hi,
I could understand you. Marcia is absolutely right about data model. I have experience in converting 3 Clipper applications in VFP6.0/7.0. We keep only business logic. We change datamodels and screens. VFP allow additional controls, like pageframe, combo box and grid, which using requiere change of old clipper datamodel. And of cource on one windows screen you can put information placed on 3-5 old screens.
My personal advice is redesign all old application and make what your customers like.