Several replied to my inquiry about copying iMovie segments from one movie to another - and sure enough, there is no great way of doing this - I was hoping for a cut and paste solution. All the wise suggestions involve some form or another of importing the files in the Media folder of the master movie into the new project. One problem is that the edited "clips" do not necessarily correspond with the DV files stored in the Media folder - the DV media files and names stay as is from the initial import. The actual tiny iMovie project file is a simple text file that keeps track of all the cuts - but this does not result in separate files being created in the Media folder - just the text-based references. Thus you can't easily edit by creating separate clips in the master movie and then import in the new movies all those edits - you instead need to import larger chunks of files and then re-edit. Again, this all depends on how the movie was imported. Not simple and involves a lot of overlap.
BUT - there is hope. I've discovered another way that may be much more intuitive. You will need QuickTime Pro to do this.
Open the Quicktime reference files in each source iMovie project (using Quicktime Pro) that is within every project file (this contains only those clips that have been moved to the Timeline window - nothing from the Clips window is contained in this Quicktime movie).
Copy and paste desired segments from these Quicktime reference files into a new Quicktime "Player"
Save this new Quicktime movie and be sure to check "Save normally (allowing dependencies)" in the Save As window. This creates references to all the source movies - but does not duplicate files (you do this next). This way you can continue to open and edit at will without dealing with huge DV files. You do have to take care NOT to alter or move any of your source movies until the final step.
When ready, Import this QT movie into a new iMovie project. You still have to go back and find all the cuts and likely re-cut - but in the end the result is one long DV stream composed potentially of many different iMovie projects.
This may be helpful for those wrestling with MANY different iMovie project and looking for ways to create a smaller composite. This is also a strategy for combining several different student movies into a master movie.
Hope this helps a few.
If you have a long DV stream (> 9 min 27 seconds) you will need to split the file up, to import it.