I'm semi-new to Rails, and the work I'm doing now requires a few Rails-based web services to interact to form the whole of our project.
Excellent. Do yourself an enormous favor and pick up a copy of Agile Web Development with Rails (2nd ed), available as a book or PDF.
It has a whole section on web services, where you'll learn how to use the web_service generator to scaffold up your web services and get to the good stuff quickly.
I have some things working using ActionWebService, but it seems as though I have to put the "whatever_api.rb" file in the /app/apis folder EVERY time I want to use the API.
That file is created for your automatically when you scaffold a web service.
If you can't afford the book, try Google for:
rails web services
Just be wary of RESTful services without checking that your .NET developers are prepared to consume them.