Alan Simes recently posted a fully C# version of Peter Walser's original IDX3D engine. You can download it here - it was built with the beta of Visual C# 2005 so you can download Express and compile it, or run the .EXE included with Alan's .ZIP to get a feel for the application. It's very performant and fun to play with - don't forget to his "load" in his sample app to import the extra 3D model of the chair. Thanks for the link, Alan! There's also a J# version available.