Here was how I did it using vb.net and crystal reports.

1. In the report, create a seperate detail section to hold your second page.  Crystal will see it as Details a & b.  In section a, set the new page after property.  This will cause the second page (details b) to print on a seperate page. 

2. Ok. The next step is to programmically tell your printer to print in duplex.  Study the code below and modify it to suite your needs.

               ' Declare an object of your report.
                Dim objReportObject As New rptTheDailySavings

                'Declare a printoptions object of the objReportObjects print option.  Set the settings.
                Dim PrintOptions As CrystalDecisions.CrystalReports.Engine.PrintOptions = objReportObject.PrintOptions
                PrintOptions.PrinterName = "Your Printer Name Here"
                PrintOptions.PaperOrientation = CrystalDecisions.Shared.PaperOrientation.DefaultPaperOrientation
                PrintOptions.PaperSize = CrystalDecisions.Shared.PaperSize.DefaultPaperSize
                PrintOptions.PrinterDuplex = CrystalDecisions.Shared.PrinterDuplex.Default
                PrintOptions.PaperSource = CrystalDecisions.Shared.PaperSource.Auto

                ' Send the report to the printer.
                objReportObject.PrintToPrinter(1, False, 1, 2)

Hope this helps.