>I have a VB.NET application, and I can't seem to make it see a C# class. I added the Class.cs file to my project. Shouldn't that work? I can see a VB.NET class in it's place.

You didn't mention if this is a winform or web app. You can mix vb and c# webform's and classes if its a web app. I'm not sure if the same techniques can be used in a winform or not. Here is an article that shows how its done.

http://www.dotnetbips.com/articles/11afc6c9-d7c7-4059-8875-489f808f1cd0.aspx