The problem is that spring-samples isn't a repository. It's a directory containing repositories. If you try to connect to the repository https://src.springframework.org/svn/spring-samples/mvc-ajax/ (I picked one project at random) in Eclipse, it will check it out with a username/password. I just tried.
The way you know which level is the repository is to keep drilling down until you see a directory called "trunk." The directory above it is the repository path.