When trying to update my DiskWarrior CD to 3.0.1, I got as far as burning the CD and it would fail before it even burned anything. The only option after a failed burn is to quit, so I went looking around and found the image it creates of the updated CD.
It is found in the /tmp/ directory, and will stay there until you hit Quit in the updater, then it will vanish. So if your burn fails through the updater, then before you hit Quit, head over to the /tmp/ directory and copy the image to another location. After quitting the updater, try and burn it using Toast or Disk Utility.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040129100857590