Visual Basic - Poner el foco a ventanas ajenas al programa

Necesito hacer un programa que ponga el foco a una ventana específica, pero esta ventana es de un programa exterior, sea Excel, o el notepad etc, en fin cualquier ventana que este disponible.

Fijate con esto, con FindWindow o FindWindowEx ubicas la ventana y con ShowWindow la muestras como la necesitas:

Public Const SW_NORMAL = 1
Public Const SW_HIDE = 0
Public Const SW_SHOWNORMAL = 1
Public Const SW_SHOWNA = 8
Public Const SW_SHOWNOACTIVATE = 4
Public Const SW_SHOWMINIMIZED = 2
Public Const SW_SHOWMINNOACTIVE = 7
Public Const SW_SHOWDEFAULT = 10
Public Const SW_SHOWMAXIMIZED = 3
Public Const SW_SHOW = 5

Public Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Public Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As String) As Long

Public Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, ByVal nCmdShow As Long) As Long