>When I create a new project, shall I just add these classes to the project, leaving them on their original location, or shall I copy them to the directory of the new project?

Leave them in a global directory and reference them. If you fix a bug in one project that uses the framework, that bug is fixed in all of them. Unless you are talking about a class that is application specific (may even be a subclass of the global ones), then create it local to the project.