This is the code to find MSN and close it but i don't know the classname and the windowname doesn't work if its not visible. So good luck 
VB Code:
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function PostMessage Lib "user32" Alias "PostMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Const SW_SHOWNORMAL = 1
Const WM_CLOSE = &H10
Private Sub Form_Load()
Dim WinWnd As Long
WinWnd = FindWindow(Classname, Windowname)
PostMessage WinWnd, WM_CLOSE, 0&, 0&
End Sub