This is a question I see very often, and you can set the paper orientation in code-behind as such:
ReportDocument.PrintOptions.PaperOrientation = CrystalDecisions.[Shared].PaperOrientation.Landscape
Crystal Reports .NET Programming
If you’re new to Crystal Reports, or just to CR .NET, this is the book you need. Part how-to, part programming reference, lots of simple examples in both C# and VB.NET.