So far i have not found how to copy part of a previous project to paste it into another video project!
When I open the second project, a popup window asks me if I want to close the former project or add the new project to it .. and no matter what I choose, it does not seems to make any difference!@#$%
Answer "yes" to adding a new project. When you now click the filmwheel under the monitor, you'll find both projects there, each of them on their own timeline. Now you can change between them by marking (or by Ctrl+F6) and copy and paste from one timeline to another with Ctrl+C and Ctrl+V.
When you are finished, you must delete your "second" project.