As I stated in my first reply, the article was written for Visual COBOL but it also applies to Net Express as the same COM client technology is supported in NX. In fact in this article it references a client demo program which is actually written for NX.
If you take the client program from the article and move it to a NX project you would be able to compile it and run it in order to access the COM server which in the example is written in VC but could be written in C# as well.