There is two way if you want a exact 1:1 copy.
Read and Burn a ISO with DVD Decrypter. The other way is to rip with with DVD Decrypter in file mode. Then use Nero to burn the DVD.
I have done two DL+R's and one was a coaster with Decrypter and the other burned fine with Nero.
I also prefer Nero as ti shows exactly where the layer change is.
I also recommend you get the latest Nero (if you want to use it) and firmware for your burner before you start burning. I have a Pioneer 109 and the latest firmware has several upgrades for DL media.