question about the selling of semi original music

drift: If you use someone else's copyrighted work, you must get their permission/pay royalties: simple as that. There are a few exceptions (fair use, for instance), but none of them apply to your case.

To give one example: Michael Jackson used about a minute of a Cleveland Symphony Orchestra recording of Beethoven's Ninth Symphony in his song "Will You Be There?" and was sued by the orchestra for copyright infringement.

Check out this site for more information. Although it is focused on the British copyright system, it has some general information about issues involving sampling and copyrights.