Vista - Back up d/dr.. premium vista, dual h/drive.

my d/dr has been filling up. when it asks me what files do i want to clean
up. i chose my files only rather than files from others. differences? i have
located the file folder norton, it says "0" . yet elsewhere its red lining
at near capacity. i chose to copy to sony dvd-r. 120m/4.7gb.. the d/drive
says it is at 4.37gb. partial copied now tells me i don't have required
space, and says try again. i inserted another disc. it partial copied then
alerts me to the same required space. am i copying the same info over and
over? and if the required space was exceeded on the first disc, should not
the second disc have started where the first left off?
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fox