I would start by opening up Internet Explorer and enter in %temp% as the
URL. Then delete everything you can, folders included that you see in
Internet Explorer. Next, you can start backing up all of your files from My
Documents to a CDR or DVDR, then delete them from drive C. Now you should
be able to copy files to drive D.
Is this a new computer? Is your D:\ drive a Restore Partition setup by your
computer manufacturer to enable you to restore your computer to a factory
default condition? If so did you make Restore DVDs of the partition?