If they are DV files, just use QuickTime to split them up. The 2GB limit is right around 9 minutes and 28 seconds. If you have QT Pro, just open the file, highlight the first 9 minutes. Do a cut, then open a new file, and paste, then save that file as a complete file, not a reference file. Repeat until you have gotten through the entire movie.
If it's not DV stream in format, instead of saving those files, choose export from the "new" file and export it to DV stream format which is what iMovie works with.
Create your iMovie project, then save it and quit. Open the project folder and move the movie segments to the Media folder. Relaunch the iMovie project. It will prompt you to add the new files to the shelf, then edit away.