Auto Control Of Dialog Window (SendMessage)

I'm trying to use Excel VBA to control a dialog box spawned from another application (in this case MS Word). The code below will obtain the window handle of the "Save As" dialog, and the SendMessage command will return the text length of the window name. This proves I can identify and communicate with the window, but I don't know how to provide a filename and click the save button. I can't find the SendMessage parameters needed to perform these actions.

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
(ByVal hwnd As Long, ByVal wMsg As Long, _
ByVal wParam As Long, lParam As Any) As Long
Private Const WM_GETTEXTLENGTH = &HE

Sub Dialog_Control()
Dim lngHwnd As Long
Dim strWindow As String
Dim varTemp As Variant
strWindow = "Save As"
lngHwnd = FindWindow(vbNullString, strWindow).......................