Using Clipmate to cut all of your project files and paste them into a correctly formatted project is probably the easiest way to do it.
Thanks, Steve, for the quick response.
I downloaded Clipmate, copied & pasted all the clips from the old project to a new one with the correct settings. This worked like a charm. I'll see whether this eliminates the errors I was getting.
Great news, ara!
Actually, I should add a post script to this issue. I jumped the gun a little in evaluating the success of Clipmate. As long as Clipmate was open in the background, I got video and audio playback in the copied clips. Once I closed Clipmate, however, my audio disappeared. Also, my transitions were no longer there. Both of these problems have been documented in other threads.
Replacing the transitions is a trivial issue compared to the alternative of starting over. The audio is a little more serious. Luckily, this has all been covered before. I found this link http://forums.adobe.com/thread/390807 that explains how to "relink" the audio to the video. In fact, a simplified version of that workaround did the job for me - I simply moved the clips used in the project to another folder. I then pointed PE to the new folder the next time I opened the project and my audio was back.