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.
[robg adds: This worked well in my testing, even on folders with spaces in their names. Note that if you use Apple's Backup app, you'll probably want to change the line that reads TARDIR=$BACKUPDIR.backup -- the .backup extension will make it appear as though the end result is a Backup package bundle. I changed the extension to simply .bkup, and then the end result is a folder, as expected.]