I recently had to burn a 704MB .avi (divX) file to a 700MB CD through my MacBook. I was pleased to find that although the default OSX Mac burner won’t overburn you can easily do this through a few terminal commands to bypass the overburn block.
1. Firstly create a directory with a short name (will be easier to type into terminal) that only contains the file you wish to burn, remove .nfo files (if a torrent file) or previews/covers leaving just the main .avi file. I called mine “movie”.
2. Open terminal (click finder and type it in if you haven’t used it before).
3. Browse to the directory above movies, enter “cd /user/downloads” where the directory containing the files you are burning is /user/downloads/movie (cd simply stands for change directory). Terminal will then display that you are in that directory. If you get stuck here because you haven’t used terminal before comment below and I will help you out.
4. Create an iso of the movies folder, in terminal enter “hdiutil makehybrid -o isofilename movie/” and your .iso will be created from the files in the folder movie. The progress will be displayed in terminal (doesn’t take long).
5. Enter your cd or DVD into the drive and burn using “hdiutil burn isofilename.iso” (while still in the same directory, which you will be if you follow the steps above). You will not be given the option of what speed to burn the disc at (in most cases this fastest setting is fine), status will again be displayed in terminal while burning and verifying the disc.
6. Once burned you can delete isofilename.iso if you don’t plan on making any more copies.

