Sub DuplexPrint()
Application.ScreenUpdating = False
Dim s As Long, e As Long, p As Long, StrPrn As String

With ActiveDocument
  s = InputBox("Start page:", "Print", "1")
  e = InputBox("End page:", "Print", .ComputeStatistics(wdStatisticPages))
  For p = s + (s Mod 2 - 1) To e Step 2
    StrPrn = StrPrn & p & " "
  Next
  StrPrn = Replace(Trim(StrPrn), " ", ",")
  If StrPrn <> "" Then
    Application.PrintOut Background:=True, FileName:="", Copies:=1, Range:=wdPrintRangeOfPages, Pages:=StrPrn
  End If
  MsgBox ("Please remove and flip over the paper stack..."): StrPrn = ""
  For p = s + s Mod 2 To e Step 2
    StrPrn = p & " " & StrPrn
  Next
  StrPrn = Replace(Trim(StrPrn), " ", ",")
  If StrPrn <> "" Then
    Application.PrintOut Background:=True, FileName:="", Copies:=1, Range:=wdPrintRangeOfPages, Pages:=StrPrn
  End If
End With

Application.ScreenUpdating = True
End Sub