In VB MDI form is created by adding MDI Form to the project and adding CHILD forms by setting MDICHILD property of the child form. In .NET there is no MDI form, any form can be made a MDI parent by setting IsMdiContainer property to TRUE.
Furthermore, there are changes in the PROPERTIES, methods and basic behavior of the MDI Forms, LIKE ABILITY to SET Background Color is not available in .NET, ability to add controls to MDI form(although they don't behave properly), ActiveForm to ActiveMdiChild, Arrange method to LayoutMdi, etc.

In VB MDI form is created by adding MDI Form to the project and adding child forms by setting MDICHILD property of the child form. In .NET there is no MDI form, any form can be made a MDI parent by setting IsMdiContainer property to TRUE.
Furthermore, there are changes in the properties, methods and basic behavior of the MDI Forms, like ability to set Background Color is not available in .NET, ability to add controls to MDI form(although they don't behave properly), ActiveForm to ActiveMdiChild, Arrange method to LayoutMdi, etc.