Imovie Stalls Playing Old Version Projects. Help!


Background: iBook
Mac OS X 10.3.9
Processor: 600 Mhz PowerPC G3
memory 640 MB SDRAM
Projects are saved on LaCie 156 GB drive

OK - I've created some rather large Imovie projects in the previous versions and they worked really well. The file I'm looking at is 2.3GB and now when I try to play it in iMovie 5 it stalls after 20 seconds with the first Clip is introduced. Sometimes the audio continues (after cutting in and out) and then it just sputters.
Are these projects irretrievable? luckily I made quicktime videos of them in the past but I'd like to edit them again and create dvd's.
please help!