rcproject - iMovie '08 Project
File Juicer can extract the JPEG thumbnails, and published videos found iMovie 08's project files.
Drop the project on File Juicer and it will search the project for the vdeos and images inside, extract them into folders organized according to file type.
You can also get to the videos yourself by control-clicking in Finder and using the "Show Contents" feature.
The thumbnails are wrapped into iMovies own format, but File Jucier will be able to get them out.