dual layer burning is just not cost effective, if your backing up DVD's then just shrink them with something like DVDShrink... but dual layer is expensive, and slow, not to mention the compatability with DVD players is very bad.
My uncle tests media for a major distributor (they supply SVP mentioned in the post above ) and he's said for a long time that dual layer is pointless for personal use.
well to copy a dual layer DVD you would use a piece of software to rip the DVD to your hard drive and de-crypt it because all DVD's are encrypted... then you would use your software to burn it to DVD.
But really its too expensive to be worthwhile, an extra 30mins and you can have compressed it to fit on a normal DVD.
thanx for the info, just had to see why it was listed as being one of the accessories on my pc and to see what it did, but it really doesn't sound as tho' it's gonna be viable to use it, cost is too prohibitive for the looks of what you can actually achieve with it.