keep in mind that you may need room on your hd that's the same size as the disk you want to burn.
the softwear may have a backup function, you tell it which files you want to back up and it does the rest. it should split some folders between disks to fill them to the max. only problem is the last disc might only have a few files on it, so I try calculate how many disks I'll need to fill the last disk half way...keeping in mind that the file system takes some room.