[MacDV] how to back up iMovies

[tamara buffalo]

Yikes I lost my movie. I spent about two weeks making an iMovie of 
florida vacation photos and video and burnt it on iDVD but then I 
thought i backed it up on an external HD and it's not there!!. I still 
have the burnt DVD.

how can  I use that burnt disk to import it back to iDVD  or iMovie to 
burn another copy or should I just use mac the ripper to copy on to Ext 
HD and burn another disk  with popcorn?

also how do I save a iMovie or iDvd project to ext HD. I have the 
latest book about Imovie and I have tried to read it but I am soooo 
confused. I get the image of the project but cant open.

  thanks in advance.
TM Buffalo