When you say you have embedded I assume you have it embedded as an OLE object.
The best way (or at least from an easy programming point of view) is to add a reference to Excel through project (that way you get to see most of the methods, properties etc of the objects)->references and select Excel Object Library.
Then include the following code:
Dim AppXL As Excel.Application, sFile As String, sPass As String
Dim AppXLWorkSheet As Excel.Worksheet
sFile = "c:\book1.xls" 'replace with your filename
Set AppXL = CreateObject("Excel.Application"

AppXL.Workbooks.Open FileName:=sFile, ReadOnly:=False, password:=sPass
AppXL.Application.DisplayAlerts = False
Set AppXLWorkSheet = AppXL.Workbooks(1).Worksheets(1)
AppXLWorkSheet.Cells(1, 1) = "Hello"
AppXL.Workbooks(1).Save
AppXL.Workbooks(1).Close
Set AppXL = Nothing
This will open a workbook called c:\book1.xls and set cell 1, 1 to be "Hello", if you need anything else please let me know.