This hint is based on this previous hint, and alluded to in this comment to that hint. I went ahead and created a DVD-spanning script using tar. Copy and paste this code into your favorite pure text editor, and save it as tar2dvd.sh. In Terminal, make it executable (chmod 755 tar2dvd.sh), and store it somewhere on your path for easy access.
To use it, just type tar2dvd.sh folder_to_backup in Terminal. For example, you could do this:
$ cd ~/Documents
$ tar2dvd.sh MyBigFolder
When the processing is done, you'll find a new folder called MyBigFolder.backup, which will contain numbered subdirectories, one per DVD.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070519051857216