Actually, if you have a DVD drive and player/decoder software installed
in your computer, you can browse a DVD just like any other disc and
copy the files from it. If you have a DVD burner, i suppose you could
copy the files to a blank.
Two issues to consider: Just about any commercial CD you come across
is going to be copyrighted. Also, right now blank DVDs with high enough
capacity to hold an average movie are selling for $30 or more, and the
copying process would probably take a couple of hours. I can drive over
to Wal*Mart and back in 25 minutes and purchase a legal copy usually
for under $20. So why bother?