a few considerations:
1. you shouldn't be using mirc to download (copyrighted) video files, since mirc is not a file sharing program, etc, etc, etc...
2. mirc has nothing to do with video/audio editing... what you're trying to do is not part of mirc functions, but belongs to other pieces of software
3. there are plenty of video editing software out there... use google and/or other search engines to find what you're looking for
4. afaik, removing background voices from videos is not possible, unless you separate audio and video and edit audio alone... this, however, requires a medium level knowledge of audio editing software
in peace and good thoughts,
/me
