How do i use the mono c sharp interpreter in mocrosoft .net?

You can use the commercial add-in, Mono Tools for Visual Studio - see http://www.mono-project.com/news/archive/2010/Mar-31.html.

Notice, though, that Mono isn't an interpreter. Mono C# programs are compiled to CIL and then just-in-time compiled to native code in a similar way to Microsoft .NET programs.