How Can I move iMovie Projects and Events?

I'd like to move my iMovie Events and Projects folders from my Mac HDD to a FW800 External

which has a lot more space on it, and to free up some space on my Mac HDD.

If I copy the folders over from my Mac HDD to my external, how do I get iMovie to recognize where they are?

I"ve looked withing preferences, but don't find a place to designate where these folders are located.

Any help or suggestions would be appreciated.