If you don't want to change your edits after inserting one project into another, then exporting an edited project as an AVI file and loading it into the other is the easiest way to do it. However, if you want to retain the ability to change the edits you have done after copying, then consider using Clipmate.
I use it often. The two limitations that I am aware of are:
1. The audio and video become unlinked.
2. Transitions aren't copied.
The procedure is a little complicated because if you do a direct copy, the audio becomes silent after you save and re-load the project.
Another option is to use Premiere Pro. You can open more than one session in it and copy between sessions. (Note that the clipboard is still cleared on closing a project, as in Premiere Elements, but that is of no consequence.)