I believe the best way is to first copy the DVD to your hard disk via the Disk Utility. Copy it over as a complete disk image, and then once it's copied, burn that image to a new DVD
I don't have a superdrive though on my PB so I have not tried this. It is, however, the method I have used to copy CD-ROMs, since I do not have any specialized burning software such as Toast.
Ruahrc