Vs3?? Do you mean VS2003?
If so, you don't need to declare a form as a MDI child.
You need to make the parent form an MDI Parent, (Set IsMDIContainer to
True)
Then the forms that are to become its children, simply set their MdiParent
property to the Parent form when instantiating them (or before displaying
then, or whenever else you want).
Cheers,
Chris.