move iMovie project to an external hard drive?

I have a project in iMovie 09 that's eating up my hard drive, as it's composed of a bunch of 1080p HD videos that I had imported from my camera into iPhoto (so in iMovie, I got at them through the iPhoto browser). I don't need the video again any time soon, so I'd like to move it onto an external hard drive. However I would like to be able to access and possibly modify it in the future, just in case. Just wondering if anyone knows how I should do this? Is there a better way than copying the project along with my entire iPhoto library to the hard drive?

I've read other discussions about moving the necessary events to a hard drive through iMovie, but my problem is that none of the source videos are in events, they're all in iPhoto. And it seems that even something like deleting a video and re-importing it confuses iMovie as to its whereabouts - a mistake I made while working on the video that was a real pain to fix - so I'm a bit nervous about moving things around.

Any ideas?