Implement sticky overlays in .NET

[DllImport("user32.dll", SetLastError: true, CharSet: CharSet.Auto)]
public def SetParent(child as IntPtr, parent as IntPtr):
    pass

def createAttachedForm(parentHandle as IntPtr):
  f = Form()
  f.Text = "My overlay"
  f.Show()
  SetParent(f.Handle, parentHandle)
  Application.Run(f)

Form.Show(IWin32Window w)