Thanks for the inputs thus far.
My computer has a 15gig drive c with the operating system on it (drive c).
I have a drive e which is about 150gig.
I've installed dvdfab plat on drive e and was working to try to do the interim copy of a dvd to drive e, but not sure I've cracked the code on how to do that yet, though I did get come full backups on some dvd's last week.
I am thinking along the lines discussed above, that perhaps I'll need up to 8.5gig free space on drive c for double-layer dvd backups.
Now this begs the question "why doesn't dvdfab platinum allow me to bypass drive c altogether and work on the humongous drive e for all interim copying during the backup?"
Maybe it does, but I can't figure out how.
In the interim, I am doing 3 successive defrags on drive c (with the 4.9 gig free space) to create the contiguous space in order to see if I can get a backup of Nova's "The Elegant Universe".
Will report back soon.