Use /Applications/Utilities/Disk Utility
Then select the "PowerBook Software" (or something like it) volume (that's just below the name of the DVD-drive).
Then click on "New Image"
(see pic)
Choose a convenient name (same as DVD), and choose where to create the image.
This will take a while.
When it's done, you can use the same "Disk Utility" to burn the image you have just made onto a DVD-R.
Good luck.