[.net] sharing files between projects?

Why not have the shared code in a class library and reference it in both projects?

Make a project named Common and add the file there. Than reference that project in both the Client and Server. I know I am just reiterating what Lundek said but I figured I would just straight out say what to do.. because I could have guessed the next question :)

Then don't add a reference to it.

I agree that having a common assembly would the preferred solution.

There's also an option if you use the "Open Existing Item" from the project menu (or right click the project and select to add existing item. In the "Add" dialog, select your foo.cs file. Rather than clicking the "Add" button, the add button also has a small arrow on it's right side. clicking that arrow will give you a "Add as link" option. That's probably what you're looking for.