You can always navigate to wellknown places in the workbook, like the first empty cell in column A. The macro recorder is very helpfull in revealing the code
;Script Options
If Not @LOGONMODE
    Break On
Else
    Break Off
EndIf
Dim $RC
$RC = SetOption("Explicit", "On")
$RC = SetOption("NoMacrosInStrings", "On")
$RC = SetOption("NoVarsInStrings", "On")
If @SCRIPTEXE = "KIX32.EXE"
    $RC = SetOption("WrapAtEOL", "On")
EndIf

;Declare variables
DIM $objExcel

;Initialize variables
;Create the Excel object, check if succeeded, else quit
$objExcel = CreateObject("Excel.Application")
If @ERROR
    Exit @ERROR
EndIf

;Code
;Show Excel
$objExcel.Visible = -1
;Open workbook with read-only password
$RC = $objExcel.Workbooks.Open("C:\test\Book1.xls",,,,"test")
;Goto cell A1 (Ctrl-Home)
$RC = $objExcel.Range("A1").Select
;Goto first empty cell (End, Arrow Down)
$RC = $objExcel.Selection.End(xlDown).Select
;Get $RC