The best way to rip and burn to dual layer media is to use DVDDecrypter in ISO Read mode. This will give you an ISO image file and a small md5 file. You can then use IMGBurn to burn to your DL disk. Load the md5 file into IMGBurn in Write mode. Set your burn speed to 2.4 or 4x for safest burning. The reason to use Decrypter and IMGBurn is that this combination will set the layer break correctly, whereas some other burning programs (cough Nero cough) don't always do so.
And always use Verbatim +R dual layer disks. There just aren't any reliable substitutes at the present time
If you have a newer dvd that has encryption that DVDDecrypter can't handle on its own, I suggest using AnyDVD to run in the background and rip with Decrypter. You could also use RipIt4Me, but its future is now in doubt.
The programs I've mentioned are free except for AnyDVD but you already have it. DVDDecrypter can be found at www.mrbass.org , among other places, and ImgBurn is at www.imgburn.com