How to copy a karaoke track to cd without the vocal part

I was given a few karaoke DVDs to copy just the instrumental tracks to CD so someone can sing along with the instrumental tracks live. I tried Switch File Converter (free version) and it did converted some songs without the vocal part but not all of them, plus some of them were cut off at the beginning or end. Is there a way to do this? What program do I need in order to do this?

How to copy a karaoke track to cd without the vocal part