How do I combine multiple projects into one project

Probably what you would like to do is just export each one of the Projects into a .m4v file using Share > Export Movie... (choose the large size).

Then in iMovie import those 35 clips into a new Event Folder. Drag those into a New Project and assemble them in the order you want them to play. You can make Empty projects in advance to hold the new Event clips after they are imported back into iMovie.

If you want those Media Browser versions they are 'squirreled away' or 'hidden' should I say in the the .rcproject file I think. That project file is in the following location:

Mac HD > Users > (your home folder) > Movies > iMovie Projects > <CTRL> + click on the project name then choose Show Package Contents. This will reveal the folders in thercproject container. The movies will be in the movies folder.

In addition to the method that Elikness provided, you can also combine movies using QuickTime Player X.

http://support.apple.com/kb/HT4024