try this:
0) backup your db first
1) to reference FileSystemObject you need to make sure the "windows script host object model" has
been referenced in your access app. in a codea code module, go to menu tools> references and ehck
that dll.
2) copy these two functions
3) need to create an import log table
tblFilesToImport - with fields
      folder (text 255),
      filename (text 255),
      FlagImport (yes/no)

4) replace "tblStagingImport" in line
 DoCmd.TransferSpreadsheet acImport, acSpreadsheetTypeExcel8, "tblStagingImport", r!folder +
r!FileName, True
with whatever table you want to import into

5) import the files by calling fnImportFile
eg
dim sFolder as string
dim sFileFrom As String, sFileTo As String
sFolder = "C:\temp\" 'whateverfolder
sFileFrom = "20080501.xls"
sFileTo = "20080510.xls"
call fnImportFile(sFolder, sFileFrom, sFileTo)

6) of course this is limited to your file names following some sort of alphaetical order

'******************************************************************************************
Function fnImportFile(sFolder as string, sFileFrom As String, sFileTo As String) As Boolean
    'import files that have been flagged in table tblFilesToImport to an import table tblStagingImport
    'replace accordingly
    Dim sTable As String, d As DAO.Database, r As DAO.Recordset
    Dim sql As String    
    'call function to import list of files to log table
    Call fnFSOGetFileList(sFolder)
   
    sTable = "tblFilesToImport"  
'-------------------------------------------------------------------------------------------------
    'if you wanted to manually check which files you wanted to import
    'sql = "select folder, filename, FlagImport from " & sTable & " where FlagImport = -1"    
'-------------------------------------------------------------------------------------------------

'-------------------------------------------------------------------------------------------------
    'criteria passed from input parameters
    sql = "select folder, filename, FlagImport from " & sTable & " where Filename between "
    sql = sql & "'" & sFileFrom & "' and '" & sFileTo & "'"    
'-------------------------------------------------------------------------------------------------
    Set d = CurrentDb
    Set r = d.OpenRecordset(sql)
    If r.RecordCount > 0 Then
        r.MoveFirst
        Do
            DoCmd.TransferSpreadsheet acImport, acSpreadsheetTypeExcel8, "tblStagingImport",
r!folder + r!FileName, True
            r.MoveNext
        Loop Until r.EOF      
    End If
    Set d = Nothing
End Function
'******************************************************************************************

'******************************************************************************************
Function fnFSOGetFileList(sFolder As String) As Boolean
    'where sFolder = "C:\myfolder\"  'whatever folder
    Dim fso As FileSystemObject
    Dim fld As folder
    Dim file As file  
    'table to store filenames
    Dim sTable As String, d As DAO.Database, r As DAO.Recordset
    Dim sql As String    
    Set fso = New FileSystemObject
    Set fld = fso.GetFolder(sFolder)  
    '-------------------------------------------------------------------------------
    'table that logs which files to import, create this table
    'it has fields folder (text 255), filename (text 255), FlagImport (yes/no)
    sTable = "tblFilesToImport"
    '-------------------------------------------------------------------------------
    'clear table entries first
    sql = "delete * from " & sTable
    Set d = CurrentDb
    d.Execute sql
    Set r = d.OpenRecordset(sTable)
   
    For Each file In fld.Files
        'whatever, insert into access table etc
        r.AddNew
            r!folder = sFolder
            r!FileName = file.Name
        r.Update
    Next file  
    Set d = Nothing
    Set fso = Nothing    
End Function
'******************************************************************************************