Here's a quick script (user defined function) that may give you a "kickstart" for this:

 Code:
Break On

$= SetExcelValue("c:\sheet.xls", "tuesday", "B5", "123")

Exit 1

Function SetExcelValue($path, $sheet, $range, $value)

 Dim $Excel
 Dim $WorkBook
 Dim $WorkSheet

 $Excel = CreateObject("Excel.Application")
 
 $WorkBook = $Excel.WorkBooks.Open($path)

 $WorkSheet = $WorkBook.Sheets.Item("Tuesday")

 $WorkSheet.Range($range).Value = $value

 $WorkBook.Save()

 $WorkSheet = 0
 $WorkBook = 0
 $Excel.Quit
 $Excel = 0

EndFunction