Is there a version of OpenForecast for Microsoft's .NET?

Yes, kind of. For OpenForecast 0.4, some minor changes were made to the OpenForecast source code to ease the automatic conversion to Microsoft's J#. If you're specifically interested in this, then be sure to get download version 0.4 (or later).

For more details on how to incorporate OpenForecast into a .NET project, see the MSDN article, Microsoft Reporting Services in Action: Extending Microsoft SQL Server 2000 Reporting Services with Custom Code , by Teodor Lachev. This article includes an excellent demonstration of how to using OpenForecast in your .NET application.

Oh, please do not contact the author of OpenForecast for details. I haven't done this myself!