How do I register a module to ruby with IronRuby and C#?
Do you mean using IronRuby from C# or C# from IronRuby?
C# from IronRuby is easy(with some caveats)
require 'C:/.../my_awesome_class.dll'
MyAwesomeClass.do_something
calling IronRuby from C# is more complicated, and you probably want to look at the docs for hosting ironruby.
The IronRuby .Net docs are a good place to get started.