I understand what you are saying now, Alin tat. It is perfectly possible to burn an image of a full Dual-Layer movie and burn it on Dual-layer writable media.
Even though you are using DL media, commercial Movie DVD's are encrypted in certain ways. That is why DVD-Shrink or DVD-Decrypter are necessary for extracting the movie to your harddrive. You can create a full iso of a movie using DVD-Decrypter. I know in DVD Shrink you can select 8.5 gig (dual layer media) with the newest version, and perhaps this will then rip the entire movie to the harddrive. I'm not sure, because I haven't burned any dual-layer media yet. Right now it's still too expensive for my needs.
But, once you do rip the full movie to your harddrive, it is perfectly possible to burn the full movie to dual-layer media using Nero.