import Microsoft.Office.Interop
Dim exl As New Excel.Application
Dim wbk As Excel.Workbook
Dim wks As Excel.Worksheet
 
wbk = exl.Workbooks.Open("C:\Test\Vorlage.xls")
wks = wbk.WorkSheets("Wertedatenblatt")
 
wks.Cells(1,1).Value = textbox1.text