I am running iMovie 9 on an non-Intel G5 (OSX 10.5.8). I just spent the last two days trying to de bug why one of my recent movies would freeze during playback in iMovie as a project file.
I read all the discussion groupd and followed all the plist file deleting recommendations to no avail. Finally I took the project and started deleting things within the project that I thought might be the source of the problem.
1) I took out all the slow motion video I had added (about 5 different clips), deleted .plist, restarted, no change project would not play.
2) Then I deleted any transition that was more compliated then just a cross dissolve. About three of them, deleted .plist file, restarted, no change .. iMovie not repsonding...force quit.
3) Then I took out the last title I added at the very end. It was the star wars type title, long paragraphs of text fading into the horizon...Deleted .plist, restrated and VIOLA... it worked.
I went on to quit iMovie and restart it again just to be sure and it worked again. So apparently there was something in that title it didin't like.
I will continue to play with the movie and go back and add in my other features and see if that makes a difference...
Hope this helps you. It's really sad the Apple can't do better with this software. . . good luck...