utilizzando il comando dos relativo.

prova un po' la seguente funzione.

codice:
Sub CombineFilesB(NewFile, ParamArray OldFiles()) 
  Dim CombinedFiles As String 
  For Each FL In OldFiles 
    If Len(CombinedFiles) Then 
      CombinedFiles = CombinedFiles & "+""" & FL & """" 
    Else 
      CombinedFiles = """" & FL & """" 
    End If 
  Next 
  Shell Environ("comspec") & " /c copy /B " & _ 
          CombinedFiles & " """ & NewFile & """", vbHide 
End Sub