Mac OS X 10.6: Burning to a recordable CD more than once
You can set up a recordable CD (such as a CD-R or CD-RW disc) to accept more disk images after it is initially burned. This way, you can burn a disk image now and add to the disc later until there is no more room on the disc. This is called “multisession” burning.
To burn a disc, you need an optical drive in your computer or connected directly to your computer. You can’t burn a disc using a remote optical drive.
To learn about multisession burning, open Disk Utility and choose Help > Disk Utility Help.