I had the exact same thing happen to me. What you need is Quicktime Pro. It's not exactly a movie-editing program, but you can at least take huge multi-GB .mov files and break them apart, or delete parts of the movie that you don't need. Then you can make smaller files of the footage you actually need, and iMovie can import them!

If you want, you can IM me files and let me know which parts you need trimmed and which parts kept, since I actually bought Quicktime Pro for that purpose. Might as well make some use out of the program and $25 I spent on it! :P