Yes, .NET predefines HRESULT values. You use them by not helping, throw a standard .NET exception just the way you would do it if a managed program uses your library. The exception's HResult property value sometimes matches a common HRESULT value if the match is obvious (like OutOfMemoryException == 0x800700E), in general a 0x8013xxxx value.
The xxxx values are widely documented and listed in the CorError.h SDK header file. IErrorInfo::GetDescription() gives you the exception's Message property value. Automagically localized, nice. You can't get the holy stack trace.
