[quote="U.S. Male"]could I make copies of my DVD on a computer and take off the sound all together, or add my own music instead? Would that be possible? Can the soundtrack of a DVD be changed when making a copy of it? Or to be on the safe side, should I tell this company to just leave the films silent in the first place.[/quote]
Later if you want to make a dvd-r/w or dvd+r/w copy of your DVD you can make a copy of it w/o sound (or subtitles, extras etc.) with
Pinnacle InstantCopy. If you want a new soundtrack you'll have to re-encode and authorize the whole thing again. Visit http://www.dvdrhelp.com/
there are tons of manuals for different programs.