Réponse acceptée !
Salut, ecoute j'y suis quand meme arrivé avec:

Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As IntPtr, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Long
Public Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As IntPtr, ByVal hWnd2 As IntPtr, ByVal lpsz1 As String, ByVal lpsz2 As String) As IntPtr

Private Const BM_CLICK = &HF5

        Dim process As Process = New Process()
        Dim Searches As Process() = process.GetProcessesByName("Search.vshost")
        Dim Search As Process
        If Searches.Length <> 0 Then
            Search = Searches(0)
            SetForegroundWindow(Search.MainWindowHandle)
            Dim SearchHandle As IntPtr = FindWindowEx(Search.MainWindowHandle, IntPtr.Zero, "Find now", Nothing)
             SendMessage(SearchHandle, BM_CLICK, IntPtr.Zero, IntPtr.Zero)

et WM_SETTEXT pour le txtbox c pas vraiment ce que je voulais faire mais cela fonctionne
Merci de ton aide
@+
youpi :)