I use nero to back up my mp3's, 700mb per disk, just drag and drop them in and burn as data, average 200 songs per disk.
6 Cdr's will back the lot up, just do them one at a time, it don't take long.
There is a bar at the bottom that shows how much space is left on the disk.
If I have misunderstood you question, Sorry.
Blakie