CD-RW are much more expensive, CD-R are cheap and very suitable
for backup. The only problem is the method/application chosen for backing up your files.
If you use File Manager to move files they will be created as Read-Only
on a CD-R. If you use XCOPY then the read only bit will not be set an
things are a lot easier.
Not having a DVD and having too much data, I'm zipping directories and
copying those to a CD-R. Not much sense in zipping photographs as they
are already compressed. Between zipping and the hardware compression
I can put a lot more data on a CD-R but am not too good at predicting how
much will go out there so I do the directories one at a time and make sure
there is enough space first.
http://www.mvps.org/dmcritchie/excel/backup.htm
which provides information on removing the read only bit, if you have already
backed up to a CD-R and the read-only bit was set..