DVDs have a css subsector which decrypts the data on the UDF partition. DVDR RWs do not have a subsector....copying such a disk to a dvdr rw would render the data unreadable. You will need to decrypt the CSS subsector as you build the flies only your hard drive.
DVD decryter, smart ripper are some of the better wares out there.
A dvd disk is
UDF Physical Partition 1.02
Audio_TS - contains audio data for SACD but usually empty for dvdvid
Video_TS - contains video data for dvd video.
It also depends on on disk size and layer break(if there is one)
4.7 disks are easy to backup....
Just rip\decode
Arrange in the audio\video folders on your hd just as they are in the origional
Personally, I would test the ripped files with powerDVD to make sure that they were decrypted correctly.
Once arranged.....make sure when you go into nero
Go into NEW
DVD
UDF Data
Physical Partition
Version: 1.02
Name your disk the same as your origional
Make sure to delete nero app under more labels
Choose the slowest writing speed(slowest is recommended)
then move the video_ts and audio_ts folders onto your image
click burn
For 8.5 dual layer dvds......
you will have to do similar.....and you will probably need nero 7 as it has better dual layer support....your layers should be evenly split
Many people have luck with dvd decrypter making dvd9 isos....but the iso mode doesnt remove the IFO video locks.....but it does decrypt the stream pretty well.....It also does new variations of CSS that smart ripper may not be able to detect.....