2. You may only have a single layer recorder.
3. Your recording software may not support DL recording.
So far there are areas you need to address. This is far from automatic and nothing in XP supports this. Find out more about your machine and software.
I have WinXp and a DVD burner on the Dell Laptop which I use as a desktop computer. When I have tried to back up My Documents on a DVD+R DL it won't accept that disk. Is there some trick to using a double layer DVD that I don't know about?