At the moment I'm trying to create a backup of one of my DVDs, however my computer (being custom built) was not bundled with any burning software. This means I have to resort to free or trial burning programs. I've found a few adequate programs for burning normal, single-layer DVDs, but I can't for the life of me figure out exactly how I'm supposed to adjust the settings so that I may burn a dual-layer DVD.

Can anyone suggest any good, free pieces of software - ones which are easily accessible - which are relatively user-friendly, and perhaps come with clear instructions?