If you'd said that in the first place...

All .NET projects compile to a .NET assembly, which contains MSIL. There is no link whatsoever to the language it was developed in. If you compile a VB.NET project to a DLL then you can reference that DLL in any .NET project, be it C#, VB.NET, J#, C++.NET, Delphi or whatever. You already do this all the time. The whole .NET Framework is written in C# and you reference those assemblies in VB.NET projects, etc. Just note that you cannot reference an application form another application. Only libraries, i.e. DLLs, can be referenced.