Not too sure what the button click code would be. However I would go with a
User Control because I don't believe you can have a Form within a Form. Here is what the code for the button clicks would probably look like:
function button1_click
DispalyPanel.Controls.Remove(Control2)
Control2.Dispose()
DispalyPanel.Controls.Add(Control1)
end function
You may have to set the display settings (such as fill and dock) in each click event to make the control fill the panel.